What's that noise? Part one: Shedding some light on the sources of noise

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Published Apr 27, 2015 | Richard Butler

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Noise Image

How would you react if I told you that the aperture and shutter speed you choose make more difference to image noise than the ISO setting? You might be surprised to discover that a lot of the noise in your images doesn't come from your camera at all: it comes from the light you're capturing.

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To really understand what's going on in your camera and, hence, how to get the best results out of it, it helps to understand a little bit about where noise comes from. Noise is widely misunderstood and yet it lies at the heart of most technical assessments of image quality and camera capability.

In simple terms, noise is any variation from the true 'signal' that you're trying to capture. Visually it's immediately recognizable as pixels of unexpected brightness or color, most easily seen in areas where you might otherwise expect a smooth result. The first thing to realize is that there are several mechanisms that contribute towards noise and that all of them can play a different role, even within a single image.

In this multi-part article, we're going to look at two major sources of noise: shot noise and electronic noise, and what they mean for the way you shoot. And because this first source of noise is so significant, we're not going to talk about electronic noise at all in this first part. By the end of both parts you should understand where noise comes from, where the strengths of your camera lie, and hence how to get the best out of it (and when it's likely to let you down).

Shot noise

Probably the most significant and certainly least recognized source of noise is what we call 'shot noise' or 'photon shot noise'. In the simplest terms, this is you being able to see the impact of light's inherent randomness.

You might remember talk of photons from science classes, and the key thing to remember is that, although we perceive light as being pretty uniform, it actually travels as a series of packets. That is: light is quantized. These packets (photons) arrive at your eye or your camera sensor at random intervals. Because of the way the eye and the brain work, you don't notice this, but when you look at a scene, you're being bombarded by little packets of randomly occurring light from every part of that scene.

'So what?' you might say. Well, let's try a little thought experiment. Rain is also a series of discrete packets, that fall randomly over time, so it makes a fairly robust metaphor for the way light behaves. So let's see what happens if we imagine trying to measure rain, using a series of test tubes.

Stand outside in the rain, with your group of test tubes covered with a plastic card. Remove the card for a fraction of a second, then quickly put it back over the tubes. You probably wouldn't be at all surprised to find no raindrops in one tube, two in another and one in the other two tubes because, just like light, raindrops occur randomly. Try the experiment again and leave the tubes exposed for a longer period of time: now you'll find all your test tubes are nearly full. If you tried measuring in detail, you might find that you had 420 drops in one tube, 380 in another and 400 in the other two tubes, but generally, you'd probably look at them and conclude they're all pretty much the same.*1

testtubes1

Short exposure

Long exposure

This randomness, even though it's raining similarly hard over all the test tubes, is noise: it's variation from the underlying signal.

An important thing to know is that, although the absolute differences in raindrops collected are larger for the longer exposure (it's a difference of 20 raindrops!), it only accounts for a small proportion of the total number (+/- 5%). With the very short exposure to the rain, the differences were only +/- 1 raindrop between test tubes, but proportionately it made a huge difference (+/- 100%). Or, to use the correct terminology, the signal you captured in the short exposure was small, relative to the amount of noise you experienced: you had much lower signal-to-noise ratio.

This is exactly how shot noise contributes to your photographs. A darker exposure gives you less chance to catch photons, so you're more likely to be able to see the random nature of them hitting your pixels. And this doesn't just apply to bright or dark exposures, it also applies to bright and dark areas within the same image. Bright parts of the image are made up from more photons hitting them during the exposure, so it's harder to perceive any variance between neighboring pixels whereas, in the darker parts of the image, fewer photons hit your sensor, so you're more likely to be able to see the underlying randomness.

The important thing to realize is that this type of noise is present whenever you try to capture light. Whether you use film or digital, medium format or a smartphone, all of the light you're capturing has shot noise built into it. And the solution is always the same: the more light you are able to capture, the less you'll be able to see that noise.

The effect of exposure on noise

Understanding the sources and effects of noise in your final image requires a good understanding of the process of capturing light and the steps it passes through on the way to your final image. The diagrams below show an image of a scene you might want to photograph, with the stripe just below the image showing the scene brightness. The light blue dots within this stripe represent the shot noise that you might experience: there are fewer of them at the dark end of the wedge, but they're more visible.

A key thing to note is that: once captured, the signal-to-noise ratio of any tone can't be improved upon.*2 It can get worse as electronic noise is added, but if you try boosting or pushing the signal, you end up boosting the noise by the same amount and the ratio stays the same. This is why your initial exposure is so important.

Scene

The diagram then shows how the exposure you choose maps the brightness of the scene to tones captured by your sensor. Because the image at the top of the diagram represents the scene, its brightness doesn't change even the exposure is changed:

Sensor

This information captured by the sensor then passes through an amplifier before being converted to digital values and written into the Raw file (in this case we're showing base ISO with minimal amplification, so the brightest tone from the sensor is being mapped to roughly the highest value in the Raw file):

Raw

Then, finally, a tone curve is applied, to map this Raw data into a final image. This can be a standard tone curve applied by your camera's JPEG engine or the result of manual Raw conversion and the adjustments made in processing software.

JPEG

Changing exposure

We'll add the contribution from electronic noise in the next article. For now, though, let's look at how noise is affected by exposure:

Exposure1

Initial Exposure, showing how the highlights, midtones and shadows in the scene are mapped all the way through to the JPEG.

Thumb Original

-1EV Exposure. The camera now captures its highlight, midtone and shadows from brighter parts of the scene.

Thumb Darker

First, let's look at what happens when you reduce the exposure (using a shorter shutter speed or narrower aperture), without making any other changes. The darker exposure captures extra highlight information and you collect each output tone from a brighter point in the scene. Shot noise remains the same if you look at any given brightness level in the final image...

...however, since you captured less light, any given area in the scene (the original highlights, midtones and shadows) will appear darker than your original exposure. And, because each part of the scene is made up from less signal, it will have a worse signal-to-noise ratio and so will appear noisier.

This becomes apparent if you try increasing the ISO to match the original image brightness using this reduced exposure...

Changing ISO

Combine this reduced exposure with increased ISO sensitivity (so that we get the same final image brightness) and the following happens:

Exposure1

Initial Exposure

Thumb Original

1EV ISO increase

Thumb Morenoise

Just as in the example above, the reduced exposure means any point in the scene appears darker on the sensor (you've captured less signal at every point in the scene). However, the camera is then applying additional amplification to make up for this, pulling the brightness back up again. And, as mentioned earlier, these amplified tones maintain their signal-to-noise ratios, which we've already seen are lower, compared to our original exposure. This result should be immediately familiar: turn the ISO up on your camera and you get the same image brightness from less exposure but at the cost of noisier images. Electronic noise can play a role in this, but the key lesson from this article is that a lot of the noise you see isn't coming from your sensor or your camera: it's inherent in the randomness of the light you captured and it's primarily dependent on the exposure you chose.

Take a look at what happens with an even higher ISO setting and it explains a lot of why your high-ISO images are noisy: most of your image is being made up from the shadow regions of your Raw file (that was captured with poor signal-to-noise ratios), amplified to be brighter.

Another interesting thing to note is that, at least initially, the camera captured the same extra highlight information that we saw when we just changed exposure. However, increasing the amplification meant they no longer fit in the Raw file, so they 'clipped' to white. This is also why higher ISO images have increasingly little dynamic range: you're amplifying-away a large chunk of the information your sensor captured. This will become relevant when we discuss some camera's dynamic range modes and when we discuss our ISO Invariance test, in the next article.

The effect of sensor size

There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor.

As we showed in our equivalence article, a full frame camera shot at 85mm F5.6 and a Four Thirds camera at 42.5mm F2.8 will have the same angle of view and the same aperture size (15.2mm diameter) and hence will be exposed to the same amount of light if exposed for the same amount of time. Or, put another way, at the same f-number (both cameras set to F2.8), the full frame camera will see four times as much light as a camera with a Four Thirds sensor, since it is exposed to the same light-per-unit-area but has a sensor with four times the area.

As a result, when you shoot two different sized sensors with the same shutter speed, f-number and ISO, the camera with the smaller sensor has to produce the same final image brightness (which the ISO standard demands) from less total light. And, since we've established that capturing more light improves your signal-to-noise ratio, this means every output tone from the larger sensor will have a better signal-to-noise ratio, so will look cleaner. Click here if you want to see an example.

Larger-001

Larger-002

Larger sensor

Smaller sensor

On a bright day, you're unlikely to notice any significant difference in the highlights and midtones since, even on very small sensors, you're usually capturing enough light to give a good signal-to-noise ratio such that the noise isn't particularly visible. However, in shadow regions, which are made up of less and less signal and, therefore, lower and lower signal-to-noise ratio, the differences will become apparent. And in lower light, an increasing part of the image will be made from tones captured with low signal-to-noise ratios and the noise will start to become obvious. This is the reason smaller sensor cameras tend to produce noisier images.

In turn, this is why we talk about different sensor sizes representing an image quality/size/price balance: because, so long as the sensor's electronic performance is similar, the effect of shot noise means that sensor size is the major determinant of image quality. Yes, pixel count can make some difference, but shot noise tends to play a much bigger role, if you compare images at the same output size.

How does this affect my photography? Exposing to the right

Whatever your sensor size, the most effective way of achieving the best results is to 'expose to the right.' It's a phrase you may have seen used, either in full or as the abbreviation ETTR. In the most simple terms, it means using the brightest exposure you can possibly get away with, without information you care about clipping to white (at which point it's impossible to recover with any color accuracy). The name comes from the appearance of the camera's histogram (the graph showing the distribution of image brightness in the image), where the right-hand side represents bright tones: you're trying to expose so your image data is as far to the right as possible without too much clipping.

This technique only really works with Raw files, since you're setting your exposure based on the brightest point in the scene, not on whether anything in the image is the 'correct' brightness. This means that you'll have to process the Raw file afterwards to adjust the image brightness the way you want it.

The other downside is that, because your camera's exposure meter and exposure guides are all based around putting scene midtones at the correct JPEG brightness level, they're not as helpful as they could be for assessing when you your Raw file has been correctly exposed to the right.

However, the benefit of this approach is that you get your sensor to capture as much light as possible without important tones clipping. This ensures that every tone you want to capture in the scene is made up of as much signal, and the least amount of shot noise contribution, as possible, and hence has the best possible signal-to-noise-ratio. This will get you the best possible noise performance and the most flexible Raw file.*3

Of course there will be situations in which there isn't enough light to expose all the way to the right (or your subject is moving so fast that you need a really fast shutter speed). In this situation you have two choices: to raise the amplification or to under-expose a lower ISO and push the Raw file later. The option you choose should depend on the specific behavior of your camera's sensor, and that's something we'll look at in more detail in part 2.

Part 2: The role of electronic noise

*1: The figures we've used in this example are deliberate: shot noise contributes a variation of +/- the square root of the signal. [Jump back to text]

*2: Technically speaking, you can improve the signal-to-noise ratio with noise reduction, which attempts to remove noise while preserving the signal. However, this typically comes at the cost of detail retention. [Jump back to text]

Sources of camera noise part two: Electronic Noise

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Published May 13, 2015 | Richard Butler, Rishi Sanyal

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Understanding how your sensor responds can open up creative options that aren't otherwise obvious. For instance, this high dynamic range scene was achieved using a single exposure, thanks to the camera's excellent noise characteristics.

In the first part of this article, we discussed the fact that a lot of the noise in a lot of your images doesn't come from your camera at all: it is you being able to see the randomness of the light that you've captured and it is almost solely dependent on how much light you were able to capture. The second source of noise is more likely to resemble what most people think of, when they think of noise: it's the background electronic noise that's added to your images by the specific camera you're using. We say this is the source of noise that most people think of because it's much easier to think of noise the way you think of background 'hum' from a Hi-Fi amplifier.

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The key thing to remember though is that, although shot noise and electronic noise stem from very different sources, with the exception of a few special cases (such as 'banding' pattern noise), they are visually indistinguishable. Noise is just variation from the expected result: aberrantly brighter or darker pixels or spurious color.

Just like with a Hi-Fi amplifier, you'll recognize that noise tends to be easier to hear during quiet patches in the music when you've got the volume turned up. In a similar manner, the electronic 'read noise' rumbles along in the dark tones of your image (where there isn't much signal) and is most likely to be visible when you've pushed your signal a lot (you're shooting at high ISO).

To better understand the behavior of different sensors, we're going to split the sources of electronic noise into two groups and consider them separately. We're going to draw the line between noise added before amplification and any added afterwards. These come in addition to light's inherent shot noise that we covered in part one.

What we're going to call Upstream read noise includes the electronic noise contributed by the pixel during the process of image capture*1. Downstream read noise includes the contribution of all the downstream electronics and all other sources after ISO amplification*2.

The reason we'll look at these two sources separately is that, while they tend not to change very much (for any particular sensor), the upstream read noise has already been added to the signal before amplification, so gets amplified along with the signal when you change ISO, whereas downstream read noise stays the same, regardless of amplification. This difference becomes important when you compare performance between sensors, as it can dictate not only the results they give but also the most effective ways to use them.

Most modern sensors have pretty low upstream read noise, the big differences between different sensor designs tend to be in how low the designers have managed to get the downstream read noise. For the rest of this article we're going to compare the behavior of two theoretical cameras: one with low upstream and low downstream read noise, and a second that differs by having higher downstream read noise, to see how and where their performance differs and consequently, how you should shoot with them. We've going to use the same tone flow diagrams that we used in part one of this article, tracking what happens to the tones in the scene, from the point of capture all the way into the final image.

At low ISOs

At base ISO, where there's no ISO amplification being applied, the low upstream read noise makes very little difference. However, the differences in downstream read noise can be seen in terms of low ISO dynamic range: a camera with lower downstream read noise will have greater low ISO dynamic range.

BaseISO-001

Base ISO - Low downstream read noise camera

Thumb Original

Base ISO - High downstream read noise camera

Thumb Original

There's every chance you won't see this in the camera's JPEGs, because even the noisiest contemporary cameras tend to have a noise floor below the darkest tone used in the JPEG. However, the best modern cameras can have several stops of additional usable dynamic range that you'll simply never see in your JPEGs. This is because JPEGs tend to have tone curves designed to create punchy images with plenty of contrast when displayed on monitors or as prints (which have relatively narrow dynamic ranges), but it means there are a lot of creative possibilities that open up if you want to shoot Raw and make use of this extra information (such as the image at the top of this page, which looked like this prior to a custom tone curve to bring out shadows).

BaseISO-001

Pushed Raw - Low downstream read noise allows high dynamic range

Thumb RawPushLL

Pushed Raw - High downstream read noise restricts dynamic range

Thumb RawPushLH

In this diagram, pushing the Raw file to pull more deep shadow information into the image (by applying a different tone curve), starts to reveal the difference in noise performance between these two sensors. On a camera with low downstream read noise, you still won't encounter its effects, even after a substantial pull from the shadows. Hover over the right-hand tab and you'll see what happens if you have higher downstream read noise: that noise gets pulled into the image.

This situation is made even worse when the downstream read noise includes a source of noise that introduces a pattern to the noise. Banding is a particular problem: because it's not totally random, it doesn't get cancelled-out by re-sizing images. Worse still, humans are especially good at recognising edges, so will tend to see patterns and find the noise much more distracting than totally random noise from other sources.

This flexibility is also valuable if you or your camera ever accidentally underexposes an image. For example, with a back-lit subject even the best metering system can sometimes get distracted by the bright background and lower the exposure. This will increase shot noise but a camera with lower downstream read noise will provide a Raw file that is more tolerant of being brightened. Using such a camera should contribute less noise than is evident in the groom's jacket in the example below.

Wedding-Backlit-After-001

Corrected image, showing additional noise and a limited tolerance for exposure correction.

Original image, Adobe Camera Raw default processing.

At high ISOs

Having said that most cameras have low upstream read noise, it starts to play a bigger role at higher ISOs, where it gets amplified, along with the signal (and all the shot noise it already contains). If we assume that a camera has a base ISO of 100, then ISO 12,800 will see any upstream read noise (and shot noise) amplified to 128 times its original, base ISO level. This will significantly dwarf any noise contribution coming from downstream read noise; so a camera whose high downstream read noise limits its low-ISO dynamic range could still have excellent high ISO performance (where shot noise and upstream read noise tend to be the limiting factors).

BaseISO-001

High ISO - Low downstream read noise has little impact. Shot noise and upstream read noise dominate

Thumb HighISO

High ISO - High downstream read noise has little impact. Shot noise and upstream read noise dominate

Thumb HighISO

Because this is a high ISO example, it uses a shorter exposure and more amplification. This can be seen in the diagram, where the scene brightness is captured as a series of darker tones on the sensor, then pushed back up by amplification before being written into the Raw file. The shorter exposure means less light is captured and all the tones from the scene are represented by small signals with poor signal to noise ratios (because of shot noise). The darker parts of the image have very little signal already which means that not only is shot noise already a large proportion of the signal, but also that even small contributions of upstream read noise will have a big impact on the signal-to-noise ratio.

The amplification means that these poorly-recorded signals (and the read noise added to them) end up as relatively bright, visible tones in the final image. However, because the downstream read noise is not amplified, its role is insignificant in comparison.

Note that the brightest tone in the Raw file and in the final image wasn't the brightest tone originally captured by the sensor. Brighter tones were captured with this exposure but then were amplified to the point that they can't be fitted in the Raw file: they've clipped and been recorded as overexposed white. Also note that all the data used to make up the final image is taken from values above the downstream read noise floor in both cases.

This means two things. Firstly, that on cameras with low downstream read noise it can make more sense to leave the ISO setting low, because you won't add significantly more noise by boosting the brightness with a tone curve, rather than by using ISO amplification, but you will retain more highlight data. By contrast, on a camera with higher downstream read noise, increasing the ISO amplification can push all your image data so that it ends up above the level of this camera's downstream read noise. This give a result that's less noisy than shooting at low ISO and brightening the image later, because brightening the dark tones would effectively amplify the downstream read noise.

Clarifying the meaning of our Raw Dynamic Range tests

These articles should also help you understand what our Raw Dynamic Range tests are showing. Our Exposure Latitude test illustrates what happens if you try to push a low ISO Raw file: a very obvious simulation of what you might do in the real world. However, it has the disadvantage that, because we have to reduce the exposure between images, we introduce more shot noise, so it's not possible to tell how much of the additional noise we see is coming from shot noise and how much is coming from read noise. As a result, you can only assess a good sensor performance by comparing cameras of the same sensor size (which will experience the same amount of light*3, meaning the differences are predominantly the result of read noise).

To solve this problem, our ISO Invariance test uses the same exposure at each setting, which means any noise differences must come from (electronic) read noise. This allows us to take a closer look at the camera's read noise contribution, without it being complicated by the effects of shot noise. This should make clear that, although it may initially seem a little unconnected to the way you shoot, it actually gives a useful insight into a camera's performance.

From this you can work out the extent to which you can choose a lower ISO setting (though still use a short exposure) and push tones selectively later, getting the same amount of noise while retaining more highlight information.

dsc 2222-002.acr

Image shot at ISO 3200, 1/100th, F8 to achieve appropriate subject brightness. Adobe Camera Raw default conversion.

Image shot at ISO 100, 1/100th, F8 pushed to match subject brightness but retain highlights. Even using the extensive highlight recovery, the sunset can't be recovered in the ISO 3200 shot.

Take home messages (TL;DR)

The main reason we wrote these articles is to address common misunderstandings about noise. As ever, the full story is a little more complicated than this. You'll hear more about quantization error in a forthcoming in-depth piece about ISO Invariance, but if you'd like to learn more about the specific sources contributing to read noise*4, then Emil Martinec's summary is a great place to continue your reading. However, we're hoping these two articles have made a couple of things clearer:

Firstly: the source of noise you encounter will depend on where you look in your image and how you shot it. Most of the noise you encounter wasn't contributed by your camera: it was shot noise from the light you captured and is primarily dictated by shutter speed, f-number and sensor size. Not pixel count.

Where your camera is contributing noise is in the darkest captured tones. At low ISOs, a camera with low downstream read noise will give you more flexible Raw files, allowing you to capture much more dynamic range than your JPEGs, opening up creative possibilities and giving files that are more tolerant of accidental underexposure.

At higher ISO, the upstream read noise and shot noise are increasingly amplified, so will appear in ever brighter tones in your image. This amplification, combined with the tiny amounts of light being captured means any small differences in upstream read noise or sensor efficiency differences will become exaggerated.

To find out how your camera behaves, our ISO Invariance tests try to show when you can expect to encounter read noise. This not only tells you how flexible your Raw files will be, but also lets you know whether a camera gives better results by upping the ISO or by keeping the same exposure values, lowering the ISO and boosting the brightness selectively, later.

Ultimately, though, we're hoping that with this information you can understand why some cameras produce less noisy images: larger sensors tend to allow more light capture, which minimizes shot noise. However, the differences in sensor performance can be enough to wipe-out these sensor size differences - especially in terms of low ISO dynamic range.

Part 1: the role of shot noise

With special thanks to Prof. Emil Martinec, Prof. Eric Fossum and Iliah Borg

Footnotes

*1 The most salient noise sources upstream of ISO amplification include reset noise, pixel amplifier noise, and dark current shot noise for longer exposures (which we won't dive into). Reset noise originates from variations in the voltages each pixel is reset to after a charge is read (ideally, they'd all be reset to the exact, same voltage). These variations - that show up as changes in intensity across neighboring pixels - can largely be mitigated by a process called correlated double sampling (CDS), which samples and subtracts the reset voltage at any pixel from the total voltage due to exposure. It can almost be thought of as a dark frame subtraction, and is very effective, lowering pixel-to-pixel variations, as well as pixel-level amplifier noise, to the level of single electrons in modern sensors. However, CDS isn't completely effective, and so a non-zero noise component still remains. For reasonable exposure lengths, any remaining reset and pixel amplifier noise post-CDS are probably the largest sources of upstream read noise. [Jump back to text]

*2 Downstream read noise includes all sources from and after, or 'downstream of,' ISO amplification. This includes noise from the programmable gain amplifier (set by your ISO setting), noise from the analog to digital conversion process, as well as any noise introduced in the pathways between all these electronic components in your camera. [Jump back to text]

*3 How much of this light a camera is able to make use of depends on its sensor efficiency, which is beyond the scope of this article. We mention it here, though, because sensors with higher efficiencies will record more of the available light during any given exposure: leading to less shot noise and a slightly cleaner result in our exposure latitude test. [Jump back to text]

*4 There are other sources of noise that are beyond the scope of this article. Thermal noise builds up with long exposures, amplifier glow can lead to 'hot spots' at the edges of your image, pixel-response non-uniformity can lead to noise even in brighter areas of your image, and quantization error further limits signal-to-noise ratio in shadows. [Jump back to text]

Grimstod

The article has one drastic issue. Sensor size is not what matters. It is the size of the pixel that matters. Read of the scientific papers out there on sensor tech and they will confirm me on this.

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Apr 28, 2022permalink

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Great Bustard

Strictly speaking, it's neither sensor size nor pixel size that matters -- it's the amount of light that makes up photo, with regards to noise.

For example, if we have two photos of the same scene, and one photo is made with more light than the other, then it will be the less noisy photo, regardless of the pixel count or sensor size.

Larger sensor systems typically have the ability to record more light than smaller sensor systems. This is accomplished by either using a wider aperture for a given exposure time (which also results in a more shallow DOF) or a longer exposure time for a given aperture (which increases the risk/severity of motion blur).

In any case, back to pixel count, here's 12 MP vs 42 MP, both at the same size:

https://www.dpreview.com/forums/post/66401510

For sure, pixel-for-pixel, the 42 MP photo is more noisy. But when comparing the same portion of the photo at the same size, then more pixels are not any worse for wear.

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Jan 28, 2023permalink

Grimstod

This metric is outside of the control or measuring stick of the sensor. At that point it is the lens that is the only thing that matters.

You point about larger sensor gathering more light is because they are paired with a larger lenses.

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Jan 30, 2023permalink

Great Bustard

In low light, yes, larger sensor systems are able to record more light only if their lenses have wider apertures, which usually results in a significantly larger, heavier, and more expensive lens. For example, a 70-200 / 2.8 on FF has an aperture that is twice as wide (4x the area) as a 35-100 / 2.8 for mFT. But the 70-200 / 2.8 for FF is significantly larger, heavier, and more expensive.

However, in good light, where one would be using base ISO, larger sensor systems are able to record more light for a given DOF. For example, if you shot a scene on mFT at 12mm f/4 1/800 ISO 100, then FF could use 24mm f/8 1/200 ISO 100 and record 4x as much light, since f/4 1/200 ISO 25 is not available for mFT sensors.

Thus, with regards to light gathering, the lens matters whenever you're above base ISO, and the sensor matters whenever you're at base ISO. However, for the same DOF and exposure time, the same total amount of light is projected on the sensor for all systems, thus the same noise.

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Jan 31, 2023permalink

Grimstod

Your math is off. 24mm f8 has an iras hole of 3mm and the same is such for the 12mm f4. They both gather the same amount of light. This is why I say this article should be rewritten. It confuses people just the way you were confused just now.

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Jan 31, 2023*permalink

Great Bustard

24mm on FF has the same [diagonal] angle of view as 12mm on mFT. 24mm f/8 on FF has the same aperture diameter/area as 12mm f/4 on mFT, thus the same intensity of light is projected on the sensor (as well as the same DOF).

However, what you missed was that 1/200 on FF is 4x longer than 1/800 on mFT. Thus, 24mm f/8 1/200 on FF will project 4x as much light on the sensor as 12mm f/4 1/800 on mFT.

Why is this relevant? If both are at base ISO, this means that FF achieves its noise advantage (normally realized as greater DR at base ISO) due to the larger sensor being able to record more light as opposed to using a wider aperture diameter on the lens.

Thus, as I said earlier, above base ISO, the noise advantage for FF comes from the lens, but at base ISO, the noise advantage of FF comes from the sensor.

So, before saying " It confuses people just the way you were confused just now", you would be served well by paying a bit more attention to what was said.

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Jan 31, 2023permalink

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Victor Engel

"There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor."

I would eliminate f-number from this, since it depends on what lens is used. Replace it with aperture diameter and you can reduce the statement to two items: shutter speed and aperture diameter. Of course there are other things, like transmissivity of the lens.

Aperture diameter is simplistically the focal length divided by the aperture number, one reason I think we should get rid of the habit of using focal length equivalents.

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Oct 15, 2021permalink

mmditter

Hmmm... while the author and others worked very hard on this well-written piece, I expected it to be much more interesting than it was. About 3 paragraphs in, I pictured myself pixel peeping- something I try to never do. To me noise is, well, like haze on an otherwise cloudless day. It's there most it the time, sometimes a lot, and sometimes a little, and every now and then, not at all. To most people, it makes very little, if any, difference in their lives.

Noise in photos can be a problem if it's excessive enough to make the image look bad to its audience. But most of the time no one but pixel peepers ever looks for it or even notices it. Also, sometimes it's introduced intentionally, just as film photographers for years pushed films like Tri-X to achieve a grainier look.

I guess I just wonder what's the point of doing such an in depth study. Do photographers today want to completely eradicate noise in images? Noise is not synonymous with bad.

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Apr 20, 2021permalink

Richard Butler

Richard Butler

The aim isn't to eradicate all noise. I wrote this piece mainly to help people understand the issue if they wanted to.

Once you understand that a lot of the noise you encounter is inherent to the light you're capturing (it doesn't come from your camera), then it can help you better understand the trade-offs we make in photography (whether in terms of the format we choose to shoot or the exposure settings we choose to use), but it's up to you what you do with that knowledge.

If nothing else, it should explain why it's impossible to completely eradicate noise from images.

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Apr 20, 2021permalink

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Tord S Eriksson

Tord S Eriksson

Very well written, Richard!

Helpful to many of us, pros as well as amateurs!

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Aug 14, 2019permalink

John K

This is where the article broke down for me:

"a full frame camera shot at 85mm F5.6 and a Four Thirds camera at 42.5mm F2.8 will have the same angle of view and the same aperture size (15.2mm diameter) and hence will be exposed to the same amount of light if exposed for the same amount of time."

The size of the sensor did not change the aperture of the lens -you used two different lenses in your example to make the field of view equal. With the exact same lens on both cameras both of them will expose the same scene at the same settings. The intensity of the image circle projected on both sensors will be exactly the same, and a digital sensor is not a single piece of light sensitive silicon like a solar cell. In short you're changing the conditions of a test in order to prove your point, and everything that follows is fundamentally flawed...

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Jan 25, 2018permalink

Richard Butler

Richard Butler

Hi John. I saw your related comment on the Equivalence article. I explained over there why you don't need to worry too much about how many pixels you have.

I'll continue my response in the comments of that article, rather than splitting the conversation over two different threads.

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Jan 25, 2018permalink

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JerryCossey

Hello, one aspect of noise that I don's see discussed is the temperature of the sensor. As the sensor heats up the noise increases. I am not sure as to how to demonstrate this effect, but do know that it is probably more of a contributor to noise in photos that one might expect. Pay attention to the heat of your camera system when you are shooting and note if you find more noise say when the weather is hotter or when you are having a long active shooting session.

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Sep 7, 2017permalink

tar4heel2

THANK YOU! Hence, the reason radio telescopes have dry-ice on the electrical circuits, to keep the noise down.

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Sep 7, 2017permalink

Richard Butler

Richard Butler

Thermal noise is certainly one of the sources of electronic noise. However, it tends not to be that significant except in the deep shadows, unless you're doing long exposure photography.

Sensors in telescopes are trying to detect very small signals often with long exposures, so it becomes much more critical to minimise every possible source of noise.

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Oct 10, 2018permalink

CamilaTL

This makes a lot of sense, the other day I was at the beach with my sonya6000 and the pictures came so noisy and I am trying to figure out why, iso was 100

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Jul 9, 2021permalink

Richard Butler

Richard Butler

Anything that results in your image being made using less light (bigger f-number, shorter/faster shutter speed) will increase the noisiness of the image.

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Jul 9, 2021permalink

CamilaTL

I was using higher shutter speed because it was super sunny, which one is worse for noise, f stop or shutter speed ? thanks

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Aug 1, 2021permalink

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AngelicBeaver

This kind of noise doesn't bother me in the slightest, but it seems to bother a lot of other people, thus camera manufacturers makes sure to smooth it all away. I wish we'd just accept and leave it. Banding or weird pattern noise is another issue entirely. A little grit is fine.

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Sep 26, 2016*permalink

MJohns

The F-stop universally determines the amount of light per unit area. What this means is that a FF camera with 4 times the pixels of an mFT camera would have the same shot noise per pixel. If the pixel counts are the same, we would see 4 times higher shot noise (assuming proportionality) in an mFT camera. But we do not. My suspicion is that it is far easier to manufacture a smaller sized sensor, so the pixels can be somewhat better quality. Further, this assumes the sensor pixels can hold maximum information in proportion to their size. This is not necessarily true. ex: The E-M1ii will offer an electronic shutter that can fire 60 frames/sec. The camera could read the sensor twice in a 30th of a sec exposure, and 4 times in a 15th sec exposure, multiplying the counts of the earlier readouts and adding them to the new ones each time. This would mean ISO 800 images could have the same shot noise level of ISO 200, but the same sensitivity as ISO 800, with extended dynamic range.

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Sep 22, 2016permalink

Great Bustard

Re: "The F-stop universally determines the amount of light per unit area. "

Yes.

Re: "What this means is that a FF camera with 4 times the pixels of an mFT camera would have the same shot noise per pixel. If the pixel counts are the same, we would see 4 times higher shot noise (assuming proportionality) in an mFT camera."

Yes, assuming the sensors have the same QE (Quantum Efficiency -- the proportion of light falling on the sensor that is recorded).

Re: "But we do not."

But we do:

https://www.dpreview.com/reviews/image-comparison?attr18=daylight&attr13_0=nikon_d4s&attr13_1=oly_em5ii&attr13_2=nikon_d4s&attr13_3=oly_em5ii&attr15_0=raw&attr15_1=raw&attr15_2=raw&attr15_3=raw&attr16_0=6400&attr16_1=1600&attr16_2=25600&attr16_3=6400&attr126_1=normal&attr126_3=normal&attr171_3=off&normalization=full&widget=1&x=0&y=0

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Nov 21, 2016permalink

Chris2210

Chris2210

@MJohns The shot noise in MFT sensors is 2 stops more than equivalent 35mm sensors because it's an inverse square rule. That is each time you halve the overall area, you halve the amount of light [= 1 Stop]. Therefore one quarter area equates to half and half again - 2 stops. That is borne out by most tests. Unfortunately the EM1ii seems to slightly underperform when compared with the best sensors at other sizes, which would imply that it's slightly less efficient than it might be.

Combining multiple exposures is a technique that can be applied to any camera, with all the benefits and pitfalls that implies. But the EM1 already offered multi-exposure [in its HDR modes] - haven't seen it touted as a technique to 'increase' sample because you might as well just double/quadruple [or whatever] the length of your exposure; and if the IS works, it's likely to give a more consistent result than combining multiple images. So it's hard to see what the advantage would be.

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Feb 17, 2017*permalink

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Pooya Rastin

Pooya Rastin

This shot noise thing which is used excessively in DPR is fundamentally flawed. Taking a picture is not like collecting raindrops. Raindrops fall in a route mostly parallel to each other. But Each spot in real life reflects or emits light in all the directions. Considert wo adjacent spots, spot A and spot B in a unoform object which we are taking a photograph of. spot A reflects billions of photons in a fraction of a second. Spot B reflects billions of photons in a fraction of a second. Spot A corresponds to pixel X in the sensor. Spot B corresponds to adjacent pixel Y in the sensor.

There is no way all the photons reflecting from spot A and entering the pixel X in the sensor in a time however small are in a substancially lower number than the number of all the photons coming from spot B and entering pixel Y.

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May 9, 2016permalink

Richard Butler

Richard Butler

When you're talking about billions of photons, it makes little difference. The absolute value of the shot noise is high but the signal is so immense that this still means a very good signal-to-noise ratio.

However, what about the darker tones in your image? The whole reason they're dark is that they're not made up of billions of photons. They're made up of few enough that the randomness of light starts to play a visible role. This is why the tiny sensors of smartphones look good in bright light but fall to bits as the light level starts to fall.

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May 11, 2016*permalink

Pooya Rastin

Pooya Rastin

Thanks for your response Richard. Something is not still clear for me. Lets suppose in 1/250 sec point 'A' reflects 1000 photons to the lens and 50% of them condense to pixel 'x'. In the same time time frame point 'B' reflects 1100 photons to the lens and 50% of them go to pixel 'y'.

So the pixel (photosite) 'x' receives 500 photons and pixel 'y' receives 550. The difference is 10% which is noticeable.

The question is: " Is it even possible that point 'A' emits 10% more light to the lens area than the adjacent point 'B' in 1/250 sec. ?"

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May 11, 2016permalink

Richard Butler

Richard Butler

The source of the randomness isn't the scattering of light, it's the randomness over time with which photons are emitted by the light source.

As I understand it, the scattering of the light (as well as their absorption of it) is part of the way they look the way they do. Objects that appear darker under bright light are scattering or absorbing more of the received light than bright, highly reflective surfaces. The scattered light never reaches your eye (or sensor) and that's one aspect of what you're trying to capture. At which point the photons are approximately like raindrops: you're only seeing the ones that travelled in a straight path from the subject to your eye/pixel.

As I say, the randomness that makes the biggest difference is the randomness of photons being emitted over time by the light source. This gives an SNR of N/Root N where N is the number of photons. Draw a graph of this relationship and see what happens as N falls (towards black/no photons).

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Sep 14, 2016*permalink

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Mohammad 7888

Thank you so much. This article was just awesome.

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Aug 24, 2015*permalink

victorjrr

Thank you Richard, very informative article!

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Jun 29, 2015permalink

forpetessake

forpetessake

ETTR is quite misguided technique as one may think that by raising ISO and moving the histogram to the right he is improving the image. While the only way to improve the noise is to increase the exposure, which has nothing to do with the ISO. The histogram doesn't show the exposure, but brightness of some jpeg that is fed to the software that draws the histogram.

They should have better advertised ETM (expose to the max), i.e. choose the maximum exposure under the existing constraints (F-stop, shutter speed, sensor saturation). Such linear constraint tasks always have the solution on the boundaries. e.g. either you choose the max F-stop the lens allows, and/or the max shutter speed that still stops the motion or prevents the camera shake, and/or the min ISO camera is capable of.

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Jun 6, 2015*permalink

Rishi Sanyal

Rishi Sanyal

Completely agree.

But could we call it ETTL? As in 'expose to the limit!'? Not to be confused with 'expose to the left'.

:)

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Sep 2, 2015permalink

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sandilands

So upon re-reading my previous post and calling it kazunga, I was reminded of what my Photography 101 instructor said in 1974. He said expose for the BRIGHTEST AND MOST IMPORTANT part of the image. I think that is the same as saying ETTR and don't worry about blowing out the spectral highlights. That was true for film and I guess it is true for digital too.

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May 23, 2015permalink

jpceulemans

Film as opposed to a digital sensor has a "shoulder": it becomes less sensitive for new photons the more saturated it is (non linear response)

That's why film is inherently better at preserving highlights and hence more tolerant to overzealous ETTR than digital

More than five years ago I started a thread about shot noise in relation to Nikon's reason for choosing lossy raw compression and everybody thought I was nuts for stating that low light levels are inherently noisy by nature

Glad that this has now been generally accepted here

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Aug 17, 2015permalink

l_d_allan

l_d_allan

IIRC, the Zone System from the film era popularized by Ansel Adams and Fred Archer taught "expose for the shadows, develop for the highlights".

('develop' involves chemicals, temperature, duration, agitation, etc.)

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Jan 15, 2016permalink

SmilerGrogan

Nothing has changed. Try to recover an overexposed highlight on a face and you'll get hideous colored and very visible boundaries between what's exposed correctly and the overexposed portion. gradual the falloff is not.

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Oct 3, 2016permalink

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Indulis Bernsteins

I think the ETTR "rule" should be changed slightly... my change in uppercase

"ETTR. In the most simple terms, it means using the brightest exposure you can possibly get away with, without information YOU CARE ABOUT clipping to white."

For example, I took a closeup photo of someone's face, with a bright background. I actually wanted the background to clip and become white.

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May 23, 2015permalink

sandilands

First my apologies for not wading through 700+ comments to date. My challenges to your thesis may have been made and defended before this.

1. Rain analogy: You discuss only the number of drops, not the size/volume of drops, the fact that rain falls in waves (a factor of light as well not addressed), and that the diameter of the tube will limit the volume of large drops collected.

2. Light packets are modified by the atmosphere, magnetic fields, and interference.

3. The light captured is from an object not the source. Some of it is reflected. some is absorbed (thus absent) and some is re-radiated.

4. Light may hit sensors as packets, but it also comes as wavelengths (hence the color of light). Most light packets are absorbed by a subject and only some wavelengths reflected. That is why leaves are green to our eye.

All of these other effects further randomize or as I prefer, smooth the randomness of light.

While your hypothesis may be correct, I suggest the net effect is negligible.

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May 23, 2015permalink

surlezi

I'm afraid you're confusing things that don't apply here.

Your interest in science and different aspects of light though laudable still need some more polishing, the article is correct, and we should all take advantage from it.

Good (re)read.

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May 23, 2015permalink

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(unknown member)

I really don't understand comments like chewdoggydog!

Knowing the physics behind doesn't make photography less artistic at all.

You may think that Turner didn't know anything about pigments and how the physics of color works? That Da Vinci didn't know anything about perspective and geometry?

Should I continue the list? Each great artist masters the physics of its domain after years of trying and working and even collaborating with scientists or engineers. This is so obvious that some people forget about it.

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May 18, 2015permalink

chewdoggydog

You folks are some damn nerds......lol. who the hell cares about all that crap. Shoot as low iso as you need to. Take more photos and less time pretending to make rockets.

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May 17, 2015permalink

Shashwat Parhi

I for one do :-) and we respect the fact that you don't...

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Aug 25, 2016permalink

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Domenick Creaco

Given that photons or their packets travel at 186,000 miles per sec, at 1/1000 sec exposure you would have photons coming in for the last 186 miles. The random distribution for photons seems to be listed as poisson, so photons arrive randomly clumped together and with short exposures the effect is more noticeable. The longer the exposure the more averaging occurs so the effect of the shot noise is reduced. My question is simple, maybe too simple but at what shutter speeds given a moderate illumination level does the effect of shot noise start to become negligible? I am into bird photography and particularly birds in flight (BIF), with pictures taken generally in broad daylight, and take photos at high shutter speed less than 1/1000 sec to limit motion blur,

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May 15, 2015permalink

(unknown member)

Whatever the speed of light, it is the number of photons that hit your sensor that you have to take into account.

Short exposure in a bright scene or long exposure in a dark one is exactly the same if you are well exposed at ISO 100.

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May 18, 2015permalink

Domenick Creaco

The rise of shot noise being visible in an image is the amount of photons that hit a pixel in the sensor with respect to the other pixels in the same sensor. Imagine photographing a purely grey or purely luminous homogeneous scene. The appearance of the shot noise is visible when other pixels in the image receive more or less photons, given rise to brighter or darker luminosity. Over a long period of time these variations will average out so the shot noise effect will cancel out according to the law of large numbers in statistics. My question is; given a moderately bright day, with a moderate f-stop at a moderate ISO, at what shutter speed will the effect of shot noise becomes noticeable. I like shooting birds in flight and have noticed some noise in the images and am not sure of the contributions of photon shot noise to sensor noise or to downstream capture noise. I try to keep the shutter speed between 1/1000 and 1/4000 sec. I use either my Sony A99 or A77ii at ISO 400-1200 LT 1/1000

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May 19, 2015permalink

(unknown member)

Shot noise does not depend on the shutter speed but on the number of photons that hit the sensor.

In other words, longer duration or wider aperture wil be the same as soon as you are well exposed at a given ISO speed because the number of photons will be the same.

Therefore if you want to reduce shot noise the only way is to lower the ISO speed. Because a low ISO speed will impose a large number of photons to be well exposed.

Then, for your specific case, I would recommand you to lower the ISO as much as possible.

:D

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May 20, 2015*permalink

Domenick Creaco

The point I am trying to make is how to choose a shutter speed in a generally well lit scene that will reduce the effect of the shot noise natural characteristic of light (not noise from the sensor or the camera's electronics). As I understand it light itself has shot noise that is distributed in a statistical manor ( I believe a poisson distribution). If we collect this light over a longer period of time the effect of shot noise will begin average out to a lower level because we are collecting more photons. The fewer photons reaching the sensor by virtue of shorter shutter speeds, the more apparent their random distribution will be, thus increasing the resulting effect of visible "grain".

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Jun 6, 2015*permalink

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Live picture

Live picture

Light is naturally wobbly from nuclear explosions on the sun. The energy of photons at the photo site varies with time, and the wavelength of the light is affected by changes in reflection of the subject if it moves during exposure. The camera tries to adjust to these variations, and does a better job if the exposure is longer. You may not want to reduce noise, because to do this the camera has to reduce detail. It is a fact that the more the noise, the more detail in the raw image. In-camera NR (or PP) can reduce details which are needed to make subjects believable.

High ISO exposures are noisier in the shadows (fewer photons available). Additional noise comes from multiplying the fewer available electrons(amplification) to make the image bright. All high ISO images have loss in detail and smaller DR, so use high ISO technique when these attributes are unimportant.

To reduce image noise, make the exposure longer or use a big aperture to capture more photons.

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May 14, 2015permalink

rishikol

rishikol

Thank you !

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Sep 8, 2015permalink

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Coheritier

Ok. I understand what you are saying. However, I have a technical question. Since photons travel in random patterns and according to your explanation; the more volume of photons that hit the sensor the better.

What happens when one adds time into the equation? Do I benefit more from having a longer exposure (slower shutter speed) than I do with a larger aperture (for any given correct exposure, whether it is TTR or not)?

My thinking is this; There is more change of having more photons hitting your sensor with a longer exposure than there is with a larger aperture. Is this correct?

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May 14, 2015*permalink

Richard Butler

Richard Butler

Both result in more photons hitting your sensor - this is the reason you get the same brightness increase by opening up your aperture by 1 stop as you do for doubling the shutter time.

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May 15, 2015permalink

CamilaTL

so if you have to use a fast shutter (f stop same) that increase noise ? thanks

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Jul 9, 2021permalink

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User4487106776

Thanks everyone for great comments...

So just let me please rephrase and revisit the question then:

I think - considering that there are relatively large number of photons per pixel (maybe hundreds and/or at least hundred+ rather than five, ten) even at 50% capture rate, I'd guess still "Shot noise" might not be barely noticeable by human eyes, if ever.

So my mew (rephtased) question is this:

Assuming something like 50% capture by sensor, at what point (number of photons per pixel) would we start noticing uneven distribution - and, hence "effects of photon bursts clumping together?

If we can figure thatone out, then maybe we can compare that to any practical level of light human eyes can sense.

ALSO, another thought - - - although each individual photons may" burst", WOULDN'T THESE "BURSTS" STILL BE RELATIVELY EVENLY DISTRIBUTED?

Thnks everyone!

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May 14, 2015permalink

stephenmattiola

stephenmattiola

I'm confused on the extra highlight part where it says it captured the same extra highlight but ultimately had to clip it to fit into the raw file, i can not seem to find where this happens. please help.

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May 14, 2015permalink

Richard Butler

Richard Butler

It happens every time you increase the ISO setting on your camera.

Set your camera in P, A or S mode and shoot an image at low ISO. Now increase the ISO setting by 1 stop. The exposure will be reduced, yet your Raw file and final image still clip at the same point as your original, low ISO exposure.

Now switch the ISO back down and match the exposure values that the camera chose for the second shot. You should notice an extra top of highlight information (and everything else 1EV underexposed). Why weren't those extra highlights in your second image?

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May 14, 2015permalink

stephenmattiola

stephenmattiola

so basically the simple way of putting it is that the since you are raising the iso and amplifying the noise the highlight is "brighter and makes it seem like there is more information?

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May 16, 2015permalink

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(unknown member)

Very interesting article ! Thanks very much DPR.

As many people here, I was wondering if the number of photons can be so low that shot noise would be significant.

Based on the so-called "sunny 16 rule", I've found that for a proper exposition on a 24 MPix FF sensor, around 50,000 photons should hit each pixel. This lead to a shot noise with an amplitude of 1.4 %.

This kind of noise amplitude should to small to be noticed. However, in darker conditions, you may have to increase the ISO speed let's say for instance 6400. It means that you have fewer photons. The corresponding shot noise amplitude will be around 3.5 %. We reach up to 14 % for ISO 100,000!

And that's the bad news: 1,000,000 ISO speed will never be as good as 100 ISO whatever the quality of the sensor because of the shot noise.

So bad...

(for those who are interseted in the computation, please mail me, you may point out some mistakes ;-) )

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May 12, 2015permalink

Richard Butler

Richard Butler

Is that figure of 50,000 photons the figure for a highlight tone or a midtone?

Dark regions will receive progressively fewer photons (hence being darker), so the SNR will drop down in darker regions of the image.

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May 13, 2015permalink

(unknown member)

I'd say for midtones. Indeed, shot noise will be greater in proportion for darker zones of a picture.

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May 13, 2015permalink

DuncanDovovan

DuncanDovovan

I did the same calculation and it was for direct sunlight!

I think the number of photons involved in catching a normal white area lit by the sun is MUCH lower than that.

And then calculate 8 stops less light for the low lights. Then SN really becomes an issue - certainly if you increase the shutter speed for example at sporting events at 1/8000 for example and with the current Megapixel hype that has fortunately stalled at the moment.

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May 13, 2015permalink

(unknown member)

For the initial photon flux I took the solar constant: 1.4 kW/m² and then I kept 1% of this value before calculating the power passing through the pupil. 1% is a quite low albedo value.

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May 13, 2015permalink

WaltFrench

I can't confirm/deny your calculations but I *WILL* note that it assumes 100% efficiency of capturing incoming photons. That's way too high.

I'm not the expert to describe the percentage that are captured, but in many sensors, a good fraction of photons fall on support electronics that are insensitive, and lost. More importantly, the fraction that hits the sensitive parts may fail to be recorded for a variety of reasons.

Using a SWAG (scientific, wild-assed guess) of 5% detection efficiency, your 1.4% noise rises to 6.3% (the square root of 1/.05). This doesn't seem unlikely for a well-exposed scene.

Note that RAW conversion techniques essentially ALWAYS employ noise-reduction. For example, a green pixel might take the average of the 4 nearest green pixels; this would smush fine details, but reduce the noise by half (again, the square root). In areas with lower signal, the RAW conversion might spread the average further, hoping to create a more acceptable image.

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May 13, 2015permalink

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User4487106776

Thanks for the article, but I'm not so sure if the theory - PHOTONS CAUSING VISIBLE SHOT NOISE? - is infact relevant...or maybe I'm missing something here:

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May 12, 2015*permalink

User4487106776

Someone asked about speed of light, and yeah sure it all depends how many "photons" there are to capture. HOWEVER, WHAT I DON'T GET IS THIS: even when it's quite DARK AND there's relatively smallER number of "photons" - wouldn't it be that there'd be STILL RELETIVELY HIGH NUMBER OF PHOTONS?

Unlike the "raindrop" analogy, the size of each photon is much much less coarse and I'd think there'll be ALMOST NEVER a case (at least in practical photography) where you'd end up with 1-0-2 kind of variations across tubes( or in this case each pixel).

Simply put, I think (even when it's very dark from human eyes' standard PLUS evn though each pixel on various sensors maybe miniscule by human standards) MY GUESS IS THAT STILL THERE'LL BE SUFFICIENTLY PLENTY OF PHOTONS PER PIXEL - enough to normalize and render any effects of these "burst" effects of photons irrelevant. (PLUS EACH "PHOTON BURST" MUST NOT BE SO COARSE and so large ENOUGH TO CAUSE NOISE)

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May 12, 2015permalink

User4487106776

Additionally, as someone mentioned (but kinda lost focus) THE SPEED OF LIGHT MIGHT HAVE BEARING TO THIS FEASIBILITY OF "PHOTON BURSTS" CAUSING NOISE AS WELL - because unless we are talking about 1 or 2 photons per pixel (which I think highly unlikely) these photons are moving at literally speed of light - meaning that a photon travels and it's as if simultaneously exists across the distnce of over 100 metres at 1/3000 exposure. So, unless theres literally only a single photon - AND I BELIEVE WE NEED A WHOLE LOT MORE for either to see or record on visible light sensors - It'll be as if countless number of them would be SIMULTANEOUSLY traveling through sensor's pixel plain.

BECAUSE IT'S EACH EXTREMELY TINY PHOTON BEHAVING AS BURST, NOT A WHOLE LOT OF BUNCH OF PHOTONS BUNDLE TOGETHER AND ACT AS A BURST.

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May 12, 2015permalink

User4487106776

Someone asked about speed of light, and yeah sure it all depends how many "photons"... HOWEVER, WHAT I DON'T GET IS THIS:

Even when it's quite DARK AND there's relatively smallER number of "photons" - wouldn't it be that there'd exist STILL RELETIVELY HIGH NUMBER OF PHOTONS?

Unlike the "raindrop" analogy, I think there'll be ALMOST NEVER a case (at least in practical photography) where you'd end up with mere a few drops kind of variations across tubes( or each pixel): each photon is too small and we need far more than a few photons to see or photograph. So, the alleged noise due to photon's burst effect must be tooo small to measure practucally?

Simply put, (even when it's very dark in human eyes PLUS even though each pixel may be miniscule by human standards) I THINK THAT STILL THERE'LL BE SUFFICIENTLY PLENTY OF PHOTONS PER PIXEL - enough to normalize and render any effects of these "burst" effects of photons irrelevant.

(EACH "PHOTON BURST" MUST NOT BE SO COARSE TO CAUSE NOISE)

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May 12, 2015permalink

User4487106776

Additionally, as someone mentioned (but kinda lost focus) THE SPEED OF LIGHT MIGHT HAVE BEARING TO THIS FEASIBILITY OF "PHOTON BURSTS" CAUSING NOISE AS WELL - because unless we are talking about 1 or 2 photons per pixel (which I think highly unlikely) these photons are moving at literally speed of light - meaning that a photon travels and it's as if simultaneously exists across the distnce of over 100 metres at 1/3000 exposure. So, unless theres literally only a single photon - AND I BELIEVE WE NEED A WHOLE LOT MORE for either to see or record on visible light sensors - It'll be as if countless number of them would be SIMULTANEOUSLY traveling through sensor's pixel plain.

BECAUSE IT'S EACH EXTREMELY TINY PHOTON BEHAVING AS BURST, NOT A WHOLE LOT OF BUNCH OF PHOTONS BUNDLE TOGETHER AND ACT AS A BURST.

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May 12, 2015permalink

DuncanDovovan

DuncanDovovan

You'd be surprised. Pixels are very very tiny. And shutter speeds of 1/1000 of a second are really very very short exposures. And dark areas really do not emit lots and lots of photons. And pixels do need lots and lots of photons to generate an electric signal.

Regarding your question about the speed of light: You cannot have x photons per second coming off your subject at your camera and then if you could change their speed, suddenly more or less than that are coming through your lens. Where would the rest be or come from?

If their speed is high, there would be a lots of distance between them. If their speed would be low, they would move closer together. But the same amount would cross a certain line.

Suppose you let light shine through a tube with water. Light moves less fast through water. But at the end of the tube, photons would move fast again through air. Does this mean the light would flicker? No.

So the speed of light has no impact here only how many photons are coming.

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May 13, 2015permalink

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stweb

Yes, how you shoot is very important.

I have already covered this (in more technical detail) on my blog:

https://stephenstuff.wordpress.com/2014/08/01/digital-photo-random-noise-and-solutions/

I usually shoot at "normal" exposure and again 1/3 or 2/3 stops over and select the best image in raw photo processing. There are differences in the shadows!

SLT.

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May 8, 2015permalink

kisvakoncl

kisvakoncl

Good article, thanks!

I'll test / try these at home.. :)

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May 6, 2015permalink

Kerni

Thank you for this great and very interesting article!

When will the other parts of this article be published?

I am looking forward to reading them.

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May 5, 2015permalink

Richard Butler

Richard Butler

I'm just trying to put the finishing touches to part 2 but some of the things that have been raised in the comments have complicated this, so I'm trying to make sure it addresses as many points as possible.

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May 6, 2015permalink

Kerni

Ok, thank you Richard!

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May 11, 2015permalink

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kimvette

kimvette

Of course - I've seen properly-exposed ISO 6400 and even 12,800 images from a 7D that were perfectly usable and ISO 400 and less photos that were full of noise from the same model, because they were underexposed and pushed too far to compensate. That being said, I would love to see truly usable extreme high ISO capability- birders/wildlife photographers and those of us interested in astrophotography would benefit tremendously, but even if sensor noise were completely licked, there will be photon noise due to the chaos nature of light.

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May 5, 2015permalink

soyo

soyo

Please, post like this deserve add articles to favorites. Thanks!

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May 5, 2015permalink

rfsIII

Here's an idea for the next article to show the real-world application of these principles. Using various exposure methods shoot four typical scenarios: A beautiful landscape a few minutes after dawn, a window-light portrait, a busy Seattle farmer's market at high noon, and rock show in a dark, smoky bar. Then show us the results.

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May 5, 2015permalink

DuncanDovovan

DuncanDovovan

Hey Richard, I know this is going to be a tough one: But in your next article, could you try to do the following:

Shot noise is really impossible to make visible, because it needs to be captured by the sensor first, which adds all kinds of different noise factors.

Would it be possible for you to calculate the number of photons caught for a certain exposure and some tonal values and then calculate the S/N ratio for those tonal values and subsequently SIMULATE that S/N for a 1:1 simulated crop of that tonal value?

So basically take the tonal value in photoshop (without noise) and add the noise based on the calculated shot noise?

That would be so great to see in your next article.

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May 5, 2015permalink

Great Bustard

This might answer, at least partially, your question:

http://www.dpreview.com/forums/post/55781353

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May 8, 2015permalink

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babart

Thanks for an interesting article that certainly states what I think is (is becoming?) the kernal of questions about noise. I.e., sensors being relatively equal the larger will give less noise problems, and exposing to the right (anathema to those of us who shot transparency film for decades) is the better way to expose digital sensors.

However, I often encounter areas of endeavor where a sizable segment of the image I want to capture is at the low end of the spectrum, and yet I don't want to clip what highlights there are. Think architectural photos of large spaces where lights would be fairly useless. How does the use of HDR affect the overall noise in those areas with less light? Yes, one is merging several images, one or two of which expose the darker areas of the scene at a brighter, less noisy, exposure value, but how does merging it with the darker frames affect the noise ratio in the darker portions of the image?

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May 3, 2015*permalink

DuncanDovovan

DuncanDovovan

Following the article, I think it might make sense to over expose the entire range to make sure the important highlights of your darkest frame are just not clipping.

After that it becomes hocus pocus, because I have no clue what algorithms HDR merge programs use to compile the end result.

Assuming the pictures have a dynamic range of 8 stops, the middle exposure has 3 stops brighter and 3 stops darker than the mid tonal value 5. If the HDR software is aware of the theory of this article, it should use information from the exposures "to the right" - so use tonal values 4, 5, 6 and 7 from the mid exposure for example (1 left, middle and 2 right).

Assuming that HDR software do not "use to the right" to secure the best parts of the pictures, perhaps it would make sense to darken all exposures before merging to force the HDR algorithm to "use to the right". The end result should be brightened again.

Would be interesting to hear Richard's input here...

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May 3, 2015permalink

babart

I don't believe any of the current HDR software is capable of "seeing to the right," which would certainly be a great idea. There are, however, ways to use two photos to combine one shot to prevent highlight clipping and a second shot to dig out the data on the dark end. An example is Photo Merge in Photoshop. However, these aren't always so great in merging, so I have used stacked images with masks to combine the photos.

It would be great if there were a merging software/plugin that would retain both the lowest and highest values between two images, then combine the two middles by blending, without the necessity for creating masks. It would also be great to have some control over that blending algorithm. Even using Smart Object snapshots (Photoshop) requires a mask to combine the two images.

Without such a program, HDR is all that's left. Hence the question. I'll be interested in the reply as well.

Thanks for writing.

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May 3, 2015*permalink

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DuncanDovovan

DuncanDovovan

Hello Richard. Thanks for being so active in the questions. I learnt a lot by reading the discussions.

In your 2nd part, could you also dive into the aspect of energy spilling from a pixel to surrounding pixels?

I notices in a few tests with over exposure, that the edge contrast between very light and very dark parts in overexposed photos becomes a bit worse. It looks like light spills over to surrounding pixels?

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May 3, 2015permalink

Oliver KMIA

Great article. Thanks.

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May 3, 2015permalink

dariva

Very good explained and helpfool, looking forward to the 2nd article.

I have learned thinks I have not be aware before.

thank you !

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May 2, 2015permalink

ftphoto

This is a very interesting article, but I feel is incomplete as it does not address how the sensor / system uses the light available across the Dynamic Range. Let me try and explain:

12 Bit with 4,096 Levels from Black (Left) to White (Right) - think Histogram

The first stop on the white side uses 2,048 bits of information.

Leaving 2,048

The next stop uses 1,024

Leaving 1,024

The next stop uses 512

Leaving 512

The next stop 261

Next stop has 130 left

Next stop has 65 left

Next stop has 32.5

As you can see as we move from brighter to darker there are less and less available bits of data to make up the shadows. Thus creating more noise in the shadow areas of an image. That is why ETTR is so important and effective.

I would like to see this addressed more accurately than how I have explained it. It is the same for all sensors though larger sensors and higher pixel counts provide more data to use therefore less noise.

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May 2, 2015permalink

Richard Butler

Richard Butler

I'll need to check on the precise reasoning, but I'm assured that this isn't why ETTRing is effective.

I think it's because, as with the test tube example in this article, a larger signal will have larger noise variation in absolute terms, and so all the additional bits you're devoting to highlights just end up describing this noise in more detail (which you tend not to be able to see, anyway).

While it's true that linear Raw devotes half the Raw file to the first stop of light, this is something of a red herring when it comes to noise, despite the long-standing articles drawing attention to it.

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May 2, 2015permalink

DuncanDovovan

DuncanDovovan

I would say the reason for having less tonal values the darker the tones become is exactly what Richard shows in his article. It does not make sense to try to make.a difference of 2048 tonal values if the S/N ratio is so bad in the darker tones... I'd say this technique of recording less and less tonal values the darker the tonal values become even reduces noise at the sacrifice of details.

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May 2, 2015permalink

ftphoto

I certainly have something to learn and look forward to Part 2.

Hopefully there will be some significant solution (compromise) to the conundrum of "Noise" we all face. Particularly if "ETTR" is not the end all be all that we had been led to believe.

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May 6, 2015*permalink

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DuncanDovovan

DuncanDovovan

Got this link from www_zeeshan_de: http://www.zeeshan.de/fotografie_apsc_vs_vollformat/0_slta99.htm

Interesting. What this guy is saying though is that his camera under exposes by default by 1.3EV. And indeed you see the effect mentioned by this article that if you over-expose by 1.3EV and then bring the light intensity back in post-processing, the resulting image has less noise - even at ISO100.

BUT. The article above suggests this guy should over-expose by at least 2 stops, because the first stop is to compensate for his under exposure. And already in the 3rd, 4th and 5th pictures that have been over-exposed by 1 stop you can see that highlight clipping took place (look at the histogram). If he would expose 2 stops or 3 as suggested by this article, he would lose information in white areas of his picture completely.

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May 2, 2015permalink

DuncanDovovan

DuncanDovovan

So, in the end the choice you have is to choose between risk of losing information in your highlights, that CANNOT be remedied by post-processing, or losing information in your lowlights, for which post-processing has some tools.

Like I said: For me "expose to the right" only makes sense in low contrast, low key images. You can reduce the noise substantially.

In normal contrast scenes, I'd just expose normally.

And in high contrast scenes, I'd even expose to the left or make HDR with multiple images!

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May 2, 2015permalink

DuncanDovovan

DuncanDovovan

I guess this becomes more of an issue if you're into astro and night photography or if you often crop out parts of your image.

Also I'm not sure how much of the noise shown is due to shot noise and how much due to read-noise. To assess that, you cannot look at RAW pictures, but you should calculate how much photons were used for the pixels. For me the distinction does not matter. The message is clear: longer exposures produce less noise - no matter where the noise comes from.

If this means you should over-expose by default to gain more information in your low lights and thereby introducing the risk of COMPLETELY loosing information in your highlights, that is a choice everybody needs to make for themselves I guess.

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May 2, 2015*permalink

ftphoto

DuncanDovovan I shoot with Fujifilm X Pro 1 and have shot with the XT-1. This system seems to have a conservative bias of at least 1 1/2 EV's to protect the highlights and Exposing To The Right works even with a sensor that is well known for low noise. This combined with my earlier post I think adds to the discussion and helps explain why noise is more prevalent in the shadows - the entire process / system has less and less data for mid tones to shadow detail available thus more noise.

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May 2, 2015permalink

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(unknown member)

Dear DPR, I appreciated this article very much. In the future, would you consider an article on lens distortion/software correction and the impact on IQ? Maybe also a little about why T-stop tails off before f/stop on many ultra-fast mirrorless lenses? (or something about vignetting and dynamic range, etc.) Basically the relationship between optics and digital sensors. Thanks!

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May 1, 2015permalink

roadtrpr

Celsus, if you have questions about those topics or want to discuss them you can post in the Photographic Science & Technology forum.

http://www.dpreview.com/forums/1061?utm_campaign=internal-link&utm_source=mainmenu&utm_medium=text&ref=mainmenu

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May 1, 2015*permalink

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mostlyboringphotog

Mr. Butler,

Pour fa vour, if you would run a test shot with Nikon 1 with their adapter for the FX lens, and same FL/f-stop/SS shot with the CX lens, FWIW, you can make me shut up :-)

Regards,

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May 1, 2015permalink

mostlyboringphotog

I only suggest Nikon 1 because I know there is an adapter that let you mount FX lens. Any other setup will do - if you can mount a Pentax MF lens on a Q camera, even a better test set up.

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May 1, 2015permalink

Richard Butler

Richard Butler

Have a look at this.

Nikon D810 with 85mm lens at F5.6

Nikon D7000 with 50mm lens at F5.6 (very nearly equivalent focal lengths, so that they're shot from essentially the same distance).

Nikon D810 in APS-C crop mode at F5.6.

Please read carefully before responding. If you prefer to think of the re-sampling in terms of magnification, that's absolutely fine.

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May 1, 2015permalink

mostlyboringphotog

Thanks for you response - I get the shot noise and why FF camera is less noisy than the crop camera. However, if you would indulge me is that the notion of larger sensor being less noisy (or smaller sensor being noisier) illogical because one could have a perfect large sensor and a perfect small sensor (neither of them is noisy) but the image from a smaller sensor is still noisier.

To me, smaller sensor is not any noisier than a larger sensor but the input to the smaller sensor was noisier. And conversely, it's not that a larger sensor is less noisier, the input to the larger sensor is less noisier due to the FF lens projecting a larger image. So if the noise level of smaller sensor is due to lower SNR input, what happen if it's illuminated with higher SNR input?

If you are saying to yourself, why did I bother to respond, I feel your pain :-(

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May 2, 2015permalink

Richard Butler

Richard Butler

On the basis the shot noise isn't coming from the sensor - it's a reflection of how much light was captured - then, strictly speaking, it's not the sensors themselves that make images from small sensors noisier.

And yes, in situations where you can provide a small sensor with more light (without overexposing), then you can get the same noise performance. However, this tends to be difficult, because, if a small sensor can cope with this extra exposure, then you can probably do the same for the large sensor, too...

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May 2, 2015permalink

DuncanDovovan

DuncanDovovan

I went on thinking down that route as well mostlyboringphotog. But then I thought this can't be true.

The lens has to make sure that f/2.8 is f/2.8 - no matter if it is attached to a FF or APS-C body.

So at f/8 the same amount of light for a specific view angle must arrive on the projection plane - no matter how big or small that sensor is.

Think of photographing a huge 18% grey wall.

If at f/8 suddenly more light would come to the sensor, then that would not be f/8 anymore.

So the amount of "rain" remains the same, but in APS-C case you have a smaller area with smaller buckets and in the FF case you have a larger area with larger buckets.

Conclusion: the larger buckets will gather more rain and therefore will have a better S/N ratio.

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May 3, 2015permalink

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DesmondD

DesmondD

After giving this more thought I'd like to ask another question based on our comparison to rain falling into tubes. Let's assume the same exposure at iso3200 - one image is taken at f2.0 and 1/1000th sec while the other is taken at f16 and 1/15th sec - both giving the same exposure. At F2.0 we have 1/1000th sec of large raindrops but they are 'let in' for such a short time the photon "packets" are more random. If we got the same final exposure at f16 and 1/15th sec would the fact that the shutter was open for longer mean that we would achieve a closer average between the 'tubes' compared to the faster shutter speed? As with rain if we put something in the rain briefly the drops are spread out but if it is left for longer eventually the whole surface is covered since there has been enough time for it to become evenly spread thereby eliminating the random aspect.

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May 1, 2015permalink

FireBeatle

When using the rain metaphor to understand the photons passing through the lens, you have to see the tubes as doing exactly the same as the lens does. Therefore, in my mind, the F2.0 lens would equate to using larger tubes versus the F16 lens opening.

So by using larger tubes for a shorter time should let in the same amount of rain as smaller tubes for longer. This would mean that the same random element is present and therefore the same SNR for both "experiments".

Think of this in another way: the rain drops (photon packets) are spread out randomly in the air at any given time. When doing either experiment, both tube sizes are exposed to the same "volume", because of the different times.

On average however, the same volume have the same expected amount of rain drops E(X) as well as the same variance VAR(X). Because you are capturing the same "volume" (or exposure) with both experiments, the E(X) and the VAR(X) are the same, so the SNR should be the same.

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May 1, 2015permalink

mostlyboringphotog

I don't think the duration of the exposure has much bearing to the shot noise within the everyday photography context. Astrophotography has all kind of other issues to deal with.

BTW, the rate at which the whole area gets wet is the same whether one looks at a large area or smaller area. So, me thinks, it's the number of the rain drops dropping and less with the number of test tubes.

To take the test tube analogy a bit further, even if only few test tubes are sparsely placed and a lot of rain drop is wasted, more rain drops mean more likely the test tubes have the accurate raindrop count.

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May 1, 2015*permalink

DuncanDovovan

DuncanDovovan

Size of the tubes DOES have an impact, because the more drops you gather in the same amount of time, the higher the S/N ratio will be (= less noise). See Poisson distribution.

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May 1, 2015permalink

mostlyboringphotog

Yes, size will have some impact but if the rain is light misty, then not much difference, I would think. And the disadvantage of larger tube is one need more rain to make some difference in the measurement. So it could go both ways.

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May 1, 2015permalink

DesmondD

DesmondD

I was thinking further about this and changing the aperture would be like having a smaller hole for the same size drops to fall through so it will smply take longer to happen. It would be an interesting test to do for those with time to play :)

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May 1, 2015permalink

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HowaboutRAW

GreB:

The Forums have their weirdnesses.

But the answer is to see the quoting convolutions a limited public (not really my term) will go thru to preserve the models of reality with which they're comfortable.

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May 1, 2015permalink

mostlyboringphotog

I presume you are referring to everyone ;-) After all, all we have are the models of reality.

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May 1, 2015permalink

HowaboutRAW

Double split up post, owing to dpr's webware.

But right we all get locked into models, and methods of description.

Great B was insisting on the near perfectness of some quantum mechanics and general relativity models that I was poking holes in.

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May 1, 2015permalink

Great Bustard

@HowaboutRAW:

Re: "Great B was insisting on the near perfectness of some quantum mechanics and general relativity models that I was poking holes in."

Demonstrating a misunderstanding of the most successful scientific theory of all time (QM -- Quantum Mechanics) is not an example of "poking holes in it". Again, I await your thread in the Photographic Science and Technology Forum:

http://www.dpreview.com/forums/1061

where you explain to those DPR members that are familiar with QM and how it applies to digital cameras that QM is wrong and thus the relationship between the total amount of light making up a photo and the noise in the photo is wrong. Feel free to throw in how GR (General Relativity) is also wrong. It should be very "entertaining". 'Course, you could start it in Off Topic, where you'll get equal input from knowledgeable people and nutters -- even more "entertaining"!

I simply cannot imagine you being shy to start such a thread -- why might that be? : )

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May 1, 2015permalink

HowaboutRAW

GB:

I'm not starting a thread.

And I wasn't claiming to know much about the claims quantum mechanics types make about digital photography.

There remain big holes in QM, one of which I already gave you.

The GR thing I already gave you too, and if you'd read, and apprehended what I posted, you'd note that I didn't say there are wholes in GR, just that it follows models from mid19th century math.

(There maybe holes in GR--I can posit one. But for now the problem is confusing the math with an explanation for the source of the curve of space/time.)

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May 1, 2015permalink

Great Bustard

@HowaboutRAW

Re: "I'm not starting a thread."

I know. : )

Re: "And I wasn't claiming to know much about the claims quantum mechanics types make about digital photography."

You mean you didn't say, "Anyhow I'm not exactly a big believer in everything quantum--maybe every time."

Re: "There remain big holes in QM, one of which I already gave you."

You mean when you claimed, "As regards the Sun and nuclear fusion--not sure that accounts for the entirety of the Sun's energy output."

Basically, all you've said is a bunch of nutter stuff, so it's no surprise, whatsoever, that you wouldn't want this discussed in a forum where people knowledgeable about these things can chime in. You want a one-on-one so that it will appear that your "knowledge" appears to be on equal footing with the one you are debating with. This is a common strategy, but easily seen through.

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May 1, 2015permalink

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mostlyboringphotog

Maybe I'm just misreading it but much of noise discussion becomes if a larger sensor is less noisy. As the shot noise is an attribute of the photons and as the SNR is a function of sqrt of number of photons (regardless of whether the photons are captured or not), the shot noise SNR is then a property of the lens and its size of image circle and not the size of a sensor.

For example, of one uses same DX lens on FF and APS-C, the photon shot noise SNR should be same; however, it's counter intuitive to think that conversely, FX lens on FF and APS-C should also have the same SNR.

So I'm very curios if the example in the article used same lens for larger sensor and for smaller sensor?

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Apr 30, 2015*permalink

Richard Butler

Richard Butler

The format the lens was designed for makes no difference at all (so long as it at least covers the format you're working on). A 50mm F2.8 is still a 50mm F2.8.

However, the question is whether the sensor is able to see all of the light (or the sensor-shaped area of it).

The diagram at the top of this page should make it clear:

An APS-C/DX sensor doesn't 'see' all the light projected by a full frame/FX lens, so the smaller sensor can't tell whether it's behind an FX or a DX lens.

And, if this is going where I think it is:

The APS-C image would have the same SNR as an APS-C crop from the full frame sensor.

However, if you used all of the full frame sensor (which would mean changing lenses, if you wanted to shoot the same scene), then the full frame image would have higher SNR and so would look cleaner when viewed at the same size.

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Apr 30, 2015permalink

DuncanDovovan

DuncanDovovan

Could you please prove your theory with crops from real pictures? Your rule to expose to the right would only allow 1 or at max 2 stops of over exposure before highlights will clip.

Could you show us a visible reduction of noise between a photo at 1/500 and one at 1/250 at same ISO and aperture where the 1/250 photo was made darker with a tone curve to match the result of the 1/500 photo?

I don't believe the difference in S/N ratio will be visible?

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Apr 30, 2015permalink

Richard Butler

Richard Butler

It's neither my theory nor have I stated any rules.

I can't run out and shoot the images right now, but I hope to include some examples in the next part of the article.

How big a difference this makes will depend on what tone you're looking at: if your signal is high enough, then you might well be able to halve it (reduce it by 1EV) and still have a high-enough SNR that the difference is negligible.

However, with a dark tone made up from very little signal, halving it will do your SNR no good at all (or, conversely, doubling the signal could be really beneficial).

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Apr 30, 2015permalink

mostlyboringphotog

"A 50mm F2.8 is still a 50mm F2.8." ; however, FX 50mm f/2.8 will project a larger image (more photons) thus higher SNR and DX 50mm f/2.8 will project smaller image (less photons) thus lower SNR.

So the larger image is cleaner every part of the image and if a crop sensor was used to take a part of cleaner image, it should still be cleaner image.

The smaller image is noisier because its lower SNR and even if one would use a larger sensor to capture it, it's still noisier, I'm thinking.

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May 1, 2015*permalink

xiao fei

xiao fei

This is a long-standing and well proven theory. A search for ETTR will give you many examples of said shutter speeds, as well as more reasons and more math to prove it. Here are two such examples.

http://schewephoto.com/ETTR/

http://digital-photography-school.com/exposing-to-the-right/

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May 1, 2015permalink

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DuncanDovovan

DuncanDovovan

Given the examples that the author uses, I assume he is addressing normal photography and not say astrophotography or night exposures.

Does the author really believe that while keeping the ISO, and aperture the same, exposing a photo 1 stop longer (assuming 2 stops will introduce clipping of highlights) and correcting this down in post-processing will actually lead to a *noticeable* (not theoretical) improvement in noise for normal portrait/landscape photography?

I'd like to see proof of that instead of theoretical talk.

Is in theory it is easy to understand he is right, but will the difference be noticeable to the human eye?

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Apr 30, 2015permalink

DuncanDovovan

DuncanDovovan

I'd like to see a comparison between a photo shot at:

ISO100 f/8 1/250 sec with a tone curve to darken

ISO100 f/8 1/500 sec

...for the dark tones, mid tones and bright tones.

I doubt there will be a visible difference.

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Apr 30, 2015permalink

DuncanDovovan

DuncanDovovan

I also think his reasoning for the sensor size is faulty. His explanation is only true if you accept that the image the lens produces is the same for both sensor sizes and therefore the smaller sensor crops out a smaller area with the same amount of pixels. Obviously the smaller pixels of the smaller sensor will then receive less pixels.

But in the real world, I will choose another lens that condenses the light to make sure the smaller sensor will "see" the same scene as the larger sensor would. This will make the amount of light available for the smaller pixels higher.

I think the actual noise increment for smaller sensors comes from the fact that the space allocated to capturing light in relation to space allocated to the structure of the chip is worse for smaller sensors. And of course if you accept the crop factor. So same ISO, speed, aperture and lens will give you more noise.

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Apr 30, 2015permalink

Great Bustard

@DuncanDonovan:

Re: "I think the actual noise increment for smaller sensors comes from the fact that the space allocated to capturing light in relation to space allocated to the structure of the chip is worse for smaller sensors. And of course if you accept the crop factor. So same ISO, speed, aperture and lens will give you more noise."

Perform the following experiment: take a "properly exposed" photo at, say, f/5.6, 1/100, ISO 200. Now put the camera in manual mode and shoot the same scene at f/5.6, 1/1600, ISO 200. Display both photos at the same brightness. What do you notice? Ideally, you will notice that the photo taken at 1/1600 is made with 1/16 as much light and thus 4x as noisy.

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Apr 30, 2015permalink

DuncanDovovan

DuncanDovovan

Yes you are right. But the difference between 1/100 and 1/1600 is hardly "exposing to the right side"! Those are 4 stops! All of your highlights will be blown out if you do that.

The method described can only mean you overexpose 1 or perhaps 2 stops. And I would like to see some samples of the noise between 1/100 and 1/200 at the same ISO and aperture, where the 1/100 picture is brought back to the same brightness using a tone curve.

To me this is highly theoretical and of no use in our daily lives as photographers...

I also believe that electronic noise is by far a bigger problem, masquerading the mentioned effect completely.

How many photons per pixel are arriving in modern day cameras for normal shots at IS0100 and 1/500 shutter speed? I would assume not 400 but rather thousands or tens of thousands? Doubling that amount will hardly result in a visible improvement of the S/N ratio?

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Apr 30, 2015permalink

DuncanDovovan

DuncanDovovan

Also, does a (in my view) theoretical and non-visible gain in S/N ratio outweigh the substantial risk of losing details in your highlights?

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Apr 30, 2015permalink

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MrGreatPic67

Thank you for this excellent article! It is giving me the clue to understand the rationale behind what I was observing already so many times in the past.

I am looking forward to the next part!

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Apr 30, 2015permalink

birdbrain

birdbrain

I'm confused, using the 'rain' analogy if we have a deluge, low f number, and we hold our test tubes under this deluge the test tubes will collect a certain amount of water. If it's a 'light' rain shower, high f number, and now hold our test tubes under this 'light shower' for a correspondingly longer time we can collect the same number of rain drops - can't we?

Sorry if i'm being a bear of little brain about this :)

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Apr 30, 2015permalink

Richard Butler

Richard Butler

Absolutely. The intensity of the rain in this metaphor is the brightness of the scene. There's nothing representing aperture (so it's fair to assume that the light/rain is unrestricted: the aperture is wide-open).

But yes, in low light/light rain you can keep your aperture open and keep the test tubes exposed for longer. In bright weather/heavy rain, you would need to shorten your exposure or introduce something to block some of the rain (an aperture).

The point is simply that light arrives at your sensor just as rain drops arrive in a test tube: as separate packets, randomly over time.

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Apr 30, 2015*permalink

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mostlyboringphotog

@By rhurani (3 hours ago)

"@mostlyboringphotog understood your question. the answer is NO. no difference, the FF lens just shed light on and around the crop sensor (what goes around is wasted)"

When I think one way I agree with you; then I think the cropped printed image of a FF sensor should still have the SNR of uncropped printed image? If so, the printed image of a "crop lens" that lets in less light than the FF lens will have less SNR than the cropped print from a FF image.

This is more of a thought experiment than if the difference if any would be visible.

It may be that I need to understand "Poisson" distribution better :)

BTW, I do not fret about the noise differences in my photos as I have other issues :(

BTW2: a radio with a larger antenna will sound louder and less noisy than a radio with a small antenna. But if you reduce the volume of a radio with a large antenna to the level of radio with a small antenna, the radio with a larger antenna will still sound clearer, no?

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Apr 30, 2015*permalink

Kerensky97

Kerensky97

I think I know where you're coming from, and you're right, but the issue on the cropped sensor is the focal length with be different even if the same photons are coming through the same lens.

So lets say I take a pic on a FF sensor with a 50mm at 1/100 f2.8 ISO100. Then I take that same 50mm lens, and put it on a crop sensor and take a picture with the same settings.

The SNR of the photons through the lens are the same, but the crop sensor is only seeing a 75mm field of view (the rest of the light is spilling off the edges of the sensor and are ignored). If you crop the 50mm FF image down to the 75mm field of view you'll see basically the same noise level between the two sensors.

The example in the article didn't compare identical lenses, the focal lengths were different so the resulting image would be the same between the FF and MFT image, leading to a bit of confusion.

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May 1, 2015permalink

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WL chandler

WL chandler

Very informative article. Learned alot from it. Time to do some experimenting.

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Apr 30, 2015permalink

joel22484

Excellent article and I am absolutely looking forward to the next part. Thank you!

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Apr 30, 2015permalink

Musicjohn

In my opinion the writer of this article is missing the real story here. The suggestion that apperture and shutter speeds have influence on the amount of noise is not correct. Making pictures at the suggested shutter speed / apperture combination will show the same amount of noise levels, even if you were to change one of the parameters (so the other changes accordingly). If I change my apperture from f/3.2 to f/8 and the shutter speed changes accordingly (at same ISO setting), I will not have two different images with two different noise levels. However, when using EV compensation and actually over-exposing, I might achieve a cleaner image. However, in a case whereby you would have to raise the ISO setting in order to make exposure to the right possible, your brighter picture may well show a lot more noise than the picture taken with the suggested shutter speed and lower ISO. So, to conclude, it is all about exposure, not about the shutter speed and apperture used.

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Apr 30, 2015permalink

rhurani

rhurani

the author did not say otherwise, you are both in agreement

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Apr 30, 2015permalink

Richard Butler

Richard Butler

And what if the 'suggested combination' isn't optimal?

Its a change in the overall exposure (defined by the combination of f-number and shutter speed) that changes the noise.

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Apr 30, 2015permalink

Kerensky97

Kerensky97

I've taken shots where increasing the ISO a stop to get the image exposed a stop to the right resulted in less noise in the finished product.

I was really confused why my ISO 100 shots were being beat by an image at ISO 200. It's cool seeing an actual article explain why noise sometimes shows up at ISO 100.

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May 1, 2015permalink

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DesmondD

DesmondD

This is an honest question: Considering the speed of light compared to the shutter speeds we use what kind of shutter speeds can actually show up the randomness of "light packets"? There must be a point where it all averages out pretty well - where is the boundary?

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Apr 30, 2015permalink

Great Bustard

The speed of light is a non-issue. The issue is how much light falls on the sensor in a given time interval. For the sake of simplicity, let's say you have a 24 MP sensor that is uniformly illuminated with 480 billion green photons during the exposure. If the QE of the sensor is 50%, this means all the pixels under the green filters will record 240 billion photoelectrons -- 10000 photoelectrons/pixel on average.

But each pixel will not record exactly 10000 photoelectrons. The standard deviation of the signal (noise) is sqrt 10000 = 100 photoelectrons/pixel. This gives a per-pixel photon NSR (noise-to-signal ratio) of 100/10000 = 1%.

Let's say we downsample the photo to 6 MP. Then each of the "pixels" in the new image file will have recorded 40000 photoelectrons on average and have a standard deviation of sqrt 40000 = 200 photoelectrons for a per-"pixel" photon NSR of 200/40000 = 0.5%.

So, there is no boundary. More light means less image noise.

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Apr 30, 2015*permalink

rhurani

rhurani

speed of light has nothing to do with this effect. it is the distribution of photons (light packets) among pixels that matters. if say 100 photons on average fall on each pixel, pixel a may get 99 photons, pixel b gets 105, pixel c gets 96 photon etc- average is 100, max difference between them is 105-100/100= 5%, here you get pixels that differ in brightness by no more that 5%. At 1000 photons the difference will be less noticed

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Apr 30, 2015permalink

DesmondD

DesmondD

I wasn't thinking when I asked this question - obviously the amount of light falling on the sensor will depend on shutter speed and aperture settings -reflected in the iso needed which will suggest how low the existing light levels are. So even if I have a shutter speed of 1 second, if the 'rain' is just a very light drizzle the 'tubes' will still not collect even amounts of 'drops' right? :) I was obviously mislead by thinking more of the actual shutter speed rather than resulting combined settings.

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Apr 30, 2015*permalink

mike703

Exactly :-)

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Apr 30, 2015permalink

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If I may, the attributes that make a great image, a great image, the level of image noise is so far below the noise threshold that a great image would not be detracted because of noise of the imaging sensor size that took the image, IMHO.

Are we not the luckiest photographers, yet?

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Apr 30, 2015permalink

Alice0102

Is there an "executive summary" for those of us that are technically challenged? My brief read leads me to believe this is something I could spend a whole lot of time concerned about when in reality I would never know if my concern and new knowledge accomplished anything at all. Why bother? Just do your best and enjoy your pictures.

Alice

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Apr 30, 2015permalink

TN Args

TN Args

Here is it: "Expose To The Right".

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Apr 30, 2015permalink

Dennis

There is. Skim the article, looking at the gold colored section headers and read the one that says:

"How does this affect my photography? Exposing to the right"

Or ... put as much light on the sensor as possible (without clipping highlights).

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Apr 30, 2015permalink

TN Args

TN Args

...."without clipping highlights that you want to keep detail in." :)

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Apr 30, 2015permalink

Great Bustard

@Alice0102:

The more light that makes up the photo, the lower the noise and higher the DR of the photo, but the greater the risk of blown highlights.

To get more light on the sensor, you either have to use a longer exposure time (which increases the risk of motion blur and/or camera shake) or a wider aperture (which results in a more shallow DOF and/or softer photo).

To maximize the IQ of the photo, all these factors must be balanced according to your aesthetics.

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Apr 30, 2015permalink

J A C S

J A C S

Actually, that article is an "executive summary" already, written by an author who undoubtedly knows much more.

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Apr 30, 2015permalink

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mostlyboringphotog

Noise is simply the unwanted part of the information that was expected, IMHO.

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Apr 30, 2015permalink

mostlyboringphotog

Is there any difference if one uses FF lens on a crop sensor compared to a crop lens on a crop sensor?

For the same f/stop and shutter speed, FF lens will let in more (total) light thus higher SNR than a crop lens, no?

This is equivalent to cutting out the crop equivalent print off the FF image vs. crop image from a crop lens.

In other words, is it the total light available or the total light captured?

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Apr 30, 2015*permalink

Great Bustard

Unless otherwise specified, comparisons are assumed to be using the same angle of view. So, for example, we would compare 85mm on [Canon] APS-C to 135mm on FF. And, yes, an 85mm lens designed specifically for APS-C would have the same angle of view as an 85mm lens designed for FF when both are mounted on APS-C.

The difference is that 135mm f/2 on FF would put 2.5x as much light on the sensor as 85mm f/2 on APS-C for a given scene and exposure time (and also have a 1.6x more shallow DOF).

It is for this reason that larger formats have lower noise than smaller formats, although the specifics of how different the noise will be will also depend on the sensor design (typically, sensors of the same generation are rather close except at the extremes).

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Apr 30, 2015permalink

mostlyboringphotog

Greetings,

I'm still trying to have someone with a more knowledge than I to chime in and say, if there is a difference between FF image that is cropped after the fact to the crop image size vs. same image taken with a crop lens and crop sensor. Clarifying this apparent paradox, SNR cannot change after the fact vs. crop sensor with a crop lens have less SNR, I think will help to lessen the controversy.

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Apr 30, 2015permalink

Great Bustard

If you use the same lens and settings on FF and a crop camera, then crop the FF photo to the same framing as the photo from the crop camera, then both photos will be made from the same total amount of light.

The IQ advantage will go to the system that put more pixels on the subject and/or had the sensor with the higher QE* and lower electronic noise**.

*The QE is the Quantum Efficiency, which is the proportion of light falling on the sensor that is recorded. For sensors of the same generation, there is remarkably little variation amongst systems regardless of sensor size, pixel count, or brand.

**The electronic noise is the additional noise added by the sensor and supporting hardware, but is very small compared to the photon noise. Thus, the electronic noise is significant only for portions of the photo made with very little light, such as deep shadows at base ISO, and progressively more of the photo as the ISO rises, becoming "significant" around ISO 3200 in modern cameras.

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Apr 30, 2015permalink

mostlyboringphotog

GB,

Thanks but it's still not clear to me if you have answered, if the noise of image of FF cropped (after the fact) to the image taken with a crop lens to the crop sensor size is equal or different.

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Apr 30, 2015permalink

Great Bustard

Let's say we have a FF sensor made with the same pixels as the sensor in a cropped DSLR (e.g. the Canon 5Ds and Canon 7D2) and took a photo of a scene from the same position with the same lens and settings, cropped the 5Ds photo to the same framing as the 7D2 photo, and displayed the photos at the same size.

The resulting photos would be all but identical.

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Apr 30, 2015permalink

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luxor2

Just great, shot noise is something else to obsess about besides bokeh. No wonder phone cameras are so popular, only the chief obsession is selfie sticks!

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Apr 30, 2015permalink

Kerensky97

Kerensky97

I know right?!

The whole reason I bought a camera with the P for Professional on the dial was so that I could take better pictures without thinking about all this.

;)

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May 1, 2015permalink

Rishi Sanyal

Rishi Sanyal

I wouldn't say you have to obsess about it... but now when you look at those low light shots and wonder where all that noise comes from, or all that smudged detail from all the noise reduction to get rid of that noise, you'll know.

And it's just kind of cool to know. :)

Also gives you an understanding of why bigger sensor tend to perform better in lower light, how smaller sensors can catch up with faster lenses, etc. And the scene/sensor/Raw/JPEG diagrams set us up for what we'll talk more about in subsequent sections: how you can't actually always compensate by giving the smaller sensors more light ad infinitum, because of finite pixel capacities.

Basically, this sets the stage for explaining many of the truths you know about (and don't know about), but don't quite exactly know the why behind.

Ultimately, understanding these things can help you make more informed decisions when considering tradeoffs of different systems, as well as tradeoffs in actual shooting/exposure.

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May 1, 2015permalink

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(unknown member)

In theory and in practice exposing to the right does indeed decrease image noise in low light shots however, it also introduces other factors that may be more detrimental to overall image quality such as lower shutter speeds (motion and camera blur induced softness) and the risk of clipping highlights. My experimentation has led me to conclude that the associated risks outweigh the benefits.

I suppose the entire exercise only proves that the benefits of ETTR are nothing to really get excited about in the real world. In reality, I would prefer the higher shutter speed with lower risk of camera shake induced blur at the cost of just slightly more noise which can easily be dealt with.

Nice article but no revelations here, sorry.

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Apr 29, 2015permalink

Matthias Hutter

There are a lot more sources than noise, and I thought you explained them very well in your A7s low light article - namely read noise and amp glow.

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Apr 29, 2015permalink

Rishi Sanyal

Rishi Sanyal

Oh, that's coming next :) I'm just glad that next time I have to write an article like that a7S one, I can just refer to this one instead of trying to stop and explain shot noise in the middle of other, already dense, text!

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May 1, 2015permalink

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dagobah

This is a nice article, thanks. We just had a discussion on this topic recently on the Pentax forum.

Sensor noise has definitely come down in the last few years -- I remember my Pentax K10D not being usable above ~ISO500. Whereas I am happy with the K-3 at ISO3200. That had to have been from the improvement of the electronic noise, no? Are there no more gains to be had on sensors of a specific size? If you're below the noise floor of shot noise, no improvement will be noticeable, and sensors wouldn't vary much in shadow noise performance.

What I've been thinking would be very useful when showing sensor performance measurements (such as DxOmark does) would be to have a curve for the sensor in question and a curve for and "ideal photon detector" of the same sensor size.

Another comment is that I am interested in ETTR -- could you maybe do a little practical guide addendum to this article at some point? Cheers.

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Apr 29, 2015permalink

HowaboutRAW

The K10D used a CCD sensor, not a CMOS sensor, like the K3.

Almost all current still cameras use CMOS sensors. The Leica ME is an exception.

Absolute purists prefer CCDs at low ISOs for colour.

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Apr 29, 2015permalink

Great Bustard

@HowaboutRAW:

The tech of the sensor, CCD vs CMOS, has nothing to do with color -- that's a common myth. Color is a function of the CFA (Color Filter Array) that covers the sensor and the noise. It is, of course, possible that CCD sensors of the past used different CFAs than modern sensors, but, again, it is the CFA, not the sensor tech, that makes this difference.

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Apr 30, 2015permalink

HowaboutRAW

G B,

Don't know that is so simple as the colour filter.

But I don't have lots of CCD still cameras to try.

People still seek out the Leica M9/ME, and it's for color. If it were simply a matter of the filter, then the M240 would have equal colour at lower ISOs. Since Leica is going to want to preserve what the M9 can do.

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Apr 30, 2015permalink

Great Bustard

Simply because both cameras are Leicas does not mean they have the same CFAs. Indeed, one of Canon's selling points for their new 5Ds is that it has a different CFA. So, again, color has nothing to do with the sensor tech (except inasmuch as color is affected by noise) -- it's all about the CFA (and, of course, how the photo is processed).

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Apr 30, 2015permalink

HowaboutRAW

GB:

Well one thing that says the filters are different, obviously, is the differing pixel count.

However, at low ISOs purists still seek CCDs and that's because of something like a clarity of sensitivity that CMOS sensors don't have. Put a filter in front of that and you get better colour, provided you're using a very good lens.

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Apr 30, 2015permalink

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mosc

DPR, can you discuss the ETTR process you use as it relates to in-camera single shot dynamic modes found on modern cameras (not multi-shot HDR gimmics)? It seems like they do many of the same things and the complexity of raw processing and manually determining exposure is far less necessary if the camera's programmers already juggle much of this automatically. Perhaps these modes are not fully developed in your eyes yet and need significant improvement?

Wouldn't it be as simple as giving users a "1 EV pull", "2 EV pull", and "3 EV pull" metering modes? Seems like if the camera can accurately meter for mid-tones then it's a simple ISO change in most cases paired with basic scaling in the JPG creation to give these outputs.

It doesn't seem complexity wise more difficult than multi-shot HDR modes except that internally the camera adjusts brightness of each to match and writes them out independently.

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Apr 29, 2015*permalink

Richard Butler

Richard Butler

Fujifilm's DR 100%, 200% and 400% modes sort of do this: they provide different exposure/amplification combinations (and we'll look at this in more detail in part 3).

However, these are still based on JPEG middle-grey metering, just offering three different choices of how much DR is provided above middle grey: they don't provide tools to help you assess how well ETTRed you are. They provide more options but still essentially leave it to guesswork.

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Apr 29, 2015permalink

mosc

What's the guesswork exactly? Which mode (normal, 100%, 200%, or 400%) you'd want to use? If Fuji, in our example here, did the metering right then they should all be the same brightness correct? The cost of picking too extreme a mode would be... I'm not sure I understand this point... noise in the darker regions?

To me, this all seems like what the user would ultimately want would be manual aperture, shutter, and exposure compensation with auto-ISO brightness where you simply turn the exposure compensation dial down to protect highlights and up to protect lowlights by however many stops you feel necessary. Perhaps through a nice WYSIWYG EVF or live-view screen showing you some key areas.

Or is the reason for this process something more complex I'm not getting that the camera's metering system and JPG engine is inadequate for?

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Apr 29, 2015*permalink

Richard Butler

Richard Butler

The point is that no camera I can think of gives you a meaningful way of telling when your Raw file is starting to clip, so at best you only have approximate tools for exposing to the right.

The DR modes of the Fujifilm give you three choices about how much of the sensor's DR you want to devote to highlights by increasingly exposing to the left. So you at least have three options about where in your Raw file to put middle grey (it would be four if you could shoot Raw at ISO 100), but you don't have any means of telling which one is optimal for the conditions you're shooting in.

There's no technical reason why you couldn't design a camera meter that obsessed about Raw highlight clipping, rather than JPEG middle grey, but it would mean abandoning the ISO standard if you went the whole hog and separated optimal exposure from the 'correct' output brightness.

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Apr 29, 2015permalink

Luego

Luego

Richard, great article...you hit the nail on the head. Unless manufacturers provide histograms based on RAW and not JPEG engines, photographers will always second guessing ETTR without highlight clipping.

I always chuckle when reading how much recovery can be achieved with RAW in PP, when all we utilize the full DR of the sensor. Many manufacturers have crippled the DR for JPEG engines. While most photographers using the JPEG histogram for ETTR, not knowing how much better SN ratio they could achieve with an RAW histogram.

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Apr 29, 2015permalink

mosc

Richard, that makes much more sense to me. Your explanation of the issue in camera metering was the key point. How metering relates to ISO levels is indeed less than ideal. People think film ISO and want to think in film ways (fixed ISO means X shutter for Y light. Click and film advance) with ISO as a constant when really it's a numerical construct on a digital sensor. I get it.

Thanks, I look forward to the rest of this piece!

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Apr 30, 2015*permalink

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yural

Brilliant article, thanks Richard.

I have one question regarding sensor size impact. Let assume we stay at exposure impact consideration (rain drop model) only and consider full size and cropped DSLR with same lens. Let take same picture with full frame, but in crop mode, and by cropped camera. (I assume the exposure should be roughly equal). Would we expect same noise than? Similar - full frame picture w/ previous exposure and image by cropped camera - what about noise in cropped area only?

Appreciate all your replays!

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Apr 29, 2015permalink

Richard Butler

Richard Butler

Assuming the same sized and similarly performing pixels, the cropped area of the full frame sensor and the APS-C sensor would look identical.

However, as soon as you use the full area of the larger sensor, you capture more signal and hence get a cleaner image.

For example, compare the Nikon D810 and D7100 in our studio scene.

The pixel-level noise is essentially the same. However, as soon as you click on the 'Web' button (top right) to view them at the same size, the additional light captured by the D810 comes into play and the image looks cleaner.

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Apr 29, 2015permalink

yural

Richard, Thanks,

I just always interested in vise verse comparison of noise, i.e. APS-C image to same image, which is done by full frame and just cropped down to APS-C size that both are captured with SAME lens and exposure.

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Apr 29, 2015permalink

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mpgxsvcd

If my scene doesn’t have any highlights that are blown at the normal/auto exposure value then is it possible that I would actually have to increase the exposure compensation in order to ETTR? In other words are there ever times when ETTR doesn’t involve decreasing the exposure compensation and is it still recommended to ETTR in those scenarios?

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Apr 29, 2015permalink

Richard Butler

Richard Butler

Absolutely.

You can always darken the data back to the correct brightness later, but every tone in your image will be made up from more light (signal), so will have a better SNR and will be cleaner.

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Apr 29, 2015permalink

mpgxsvcd

Then Auto ETTR will become the next Megapixel war in the future. Except for this time it will actually bring real benefit to the photographs and videos.

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Apr 29, 2015permalink

Great Bustard

@mpgxsvcd:

"Auto ETTR" is simply more intelligent metering. The thing is that the DR of a scene is often far greater than the DR of the sensor, so either highlights get blown or shadows get blocked, and the camera can't know what balance the photographer wants to make.

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Apr 30, 2015permalink

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flysurfer

flysurfer

A very nice and useful article, Richard! As you know, I have been writing about ISOless photography for quite some time, as it's an integral part of all my workshops, so seeing DPR pushing this topic with improved test procedures ("ISO-invariance") and general articles like this one is a wonderful thing. These texts as mandatory reading matter for my delegates (at least those who speak English), so keep them coming.

It's high time that old thinking and antiquated sensor technology are pushed overboard. It's also good to reward camera makers who choose the ISOless sensor path (but often fail to communicate the advantages out of fear that it might confuse the customer who tends to stick with simple solutions and what he thinks he knows from the film era).

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Apr 29, 2015permalink

exdeejjjaaaa

exdeejjjaaaa

and as most of people using ACR/LR there shall be a homage to hue twists = http://dcptool.sourceforge.net/Hue%20Twists.html

credit for the article (and dcptool) to SandyMc(Guffog)

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Apr 29, 2015permalink

(unknown member)

More on the subject:

https://luminous-landscape.com/the-optimum-digital-exposure/

http://digitaldog.net/files/ExposeForRaw.pdf

https://luminous-landscape.com/precise-digital-exposure/

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Apr 29, 2015permalink

Just Ed

Just Ed

Awesome article! Thank you DPR for sharing this with your readers. Am anxiously awaiting part 2.

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Apr 29, 2015permalink

D Gold

D Gold

This is a great article. I use my Nikon D610 for astrophotography and talk about a shot noise challenge. I am actually pretty happy with my results so far.

I have been trying different ISO speeds on imaging and for now have settled at 800 as being the best amplification for long exposures, (I am shooting up to 300 seconds per frame and stacking the images).

I was hoping in your next article you all talk about fixed pattern noise. The sensor/image processing train in my D610 seems really good in this regard.

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Apr 29, 2015permalink

esasjl

Thank you for an excellent article that is a very nice visualisation of a random process (√n 'error' etc), something familiar to any who measure photons of any energy. It's interesting that we call the real signal (i.e., the statistical randomness of photon distribution) 'noise' just because it doesn't agree with our large-scale perceptions. The real noise comes from what we expect (or aspire to), not the basic physics; our camera sensors are just responding accurately to the photon flux. Maybe we should celebrate the presence of randomness as the true refelection of the natural world it is and make a positive of the character this gives to images?

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Apr 29, 2015permalink

Roland Boyer

Sorry for bad English I am French / In my opinion, you are wrong when saying :" a full frame camera shot at 85mm F5.6 and a Four Thirds camera at 42.5mm F2.8 will have the same angle of view and the same aperture size (15.2mm diameter) and hence will be exposed to the same amount of light if exposed for the same amount of time".... Ok for the same angle of view, but i disagree about the "same amont of light" Because on the full frame camera, le light need twice the way to focus at 85 mm and decraese by 4 , compared to focus at 42,5mm! That why we need bigger diameter for the same F-stop on full frame... What is changing is size of pixel (or number of "silver-grain" on film! So you're wright only about le light passing through the lens, and not le light on the sensor or film!

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Apr 29, 2015permalink

Richard Butler

Richard Butler

We'll come to the effect of pixel size in part two (since the difference comes down to read noise, not shot noise).

But the most important factor is the light passing through the lens, because most sensors of any given age are (broadly) similarly good at making use of that light.

F-number tells you light per unit area (cancelling out the effect of sensor size), which obscures the reason why bigger sensors tend to be better (more light).

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Apr 29, 2015*permalink

Roland Boyer

I see what you mean! Very intesting subject! Awaiting for the second part

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Apr 29, 2015permalink

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P Johnson

Sigma cameras with Foveon sensor are said to produce no noise whatsoever at 50 ISO which seems to be true except for very dark long exposre night shots that I tested but they were probably underexposed since the camera didn't provide long exposure time enough but there wasn't much information to detect anyway (Sigma DP1s).

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Apr 29, 2015permalink

Felix E Klee

Felix E Klee

AFAIK when you shoot the DP1s at ISO 50, the image is actually captured at ISO 100, then corrected EV-1 in software. See previous discussion: Certain Sigma Foveon cameras, if not all, have fixed ISO.

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Apr 29, 2015permalink

P Johnson

Well then the sensor is noise free at 100 ISO if the camera is set to 50 ISO.

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Apr 29, 2015*permalink

Zdman

I believe AFE was introduced to give actual analogue amplification instead of digital as higher ISO shots (from SD15 on I think) but before that they were essentially fixed ISO with digital amplification. ISO 50 is actually ISO 100 overexposed as Felix said.

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Apr 29, 2015*permalink

J A C S

J A C S

Noise free images are impossible, as the article explains. Noise free Sigma images are even less possible.

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Apr 30, 2015permalink

P Johnson

As said, I can't find any noise in my Sigma DP1s' images taken with camera set at 50 ISO. I've really tried hard. This article simply doesn't apply to Sigma sensor technology. Having said that, other sensors have other advantages and will eventually fill this gap.

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Apr 30, 2015*permalink

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Clint Dunn

Clint Dunn

I haven't worried about noise in over 6 years....

High ISO, surely the most overrated of camera specs.

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Apr 29, 2015permalink

GEAH

GEAH

It's the most underrated of camera specs for me.

It all depends on what you shoot. Try to shoot a hyperactive rock band in a room lit by a single 100W bulb and get back to me about how important ISO is.

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Apr 29, 2015permalink

mediasorcerer

mediasorcerer

It certainly can be a great asset to have a camera with a sensor that produces cleaner files at ^ iso, however, as this poster mentioned, it depends on the users potential usage scenario, technique and expectations.

In the case described above, hes absolutely right, however, the technical compromise [if u choose to view it as that] is usually less pixels on sensor to achieve higher iso rating.[according to my limited understanding and the ^iso cameras available atm]

It is certainly a very valid and correct point to make/

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Apr 29, 2015permalink

D Gold

D Gold

>High ISO, surely the most overrated of camera specs

Try shooting astrophotography images with a noisy image train - it just makes things harder when you're dealing with 10 photons per second, if your lucky. I'll take all the improvements that can be generated.

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Apr 29, 2015permalink

Clint Dunn

Clint Dunn

I should add the second most overrated spec is fps......cue the tirade of sports shooters.

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Apr 30, 2015permalink

Clint Dunn

Clint Dunn

GEAH - If you can't shoot rock bands with ANY camera made in the last 7 yrs then you're lucky you weren't around in the days of film.

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Apr 30, 2015permalink

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eddychan008

85mm 5.6 lens and 42.5mm 2.8 with same diameter of aperture.... that's right because this is how the aperature value is defined.

A 85mm lens at 2.8 may capture 4 times as much light as 42.5mm at 2.8 but at the same time this light is distributed over 4 times as big an area so to each pixel of each respective sensor still get the same amount of light on it if exposed for same shutter speed, same iso and same "aperture".

It is not the same as saying the smaller sensor has to bring the brightness level up with less total light captured ?

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Apr 29, 2015permalink

sina_hml

That is exactly what I'm thinking and nobody is explaining why we might be wrong.

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Apr 29, 2015permalink

Zdman

Sorta. The golden rule is quite easy for a given depth of field the amount of photons captured remains the same. So in the above example more light falls on the full frame in total but at the cost of depth of field.

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Apr 29, 2015permalink

mosc

I think the best way to look at is is physical aperture size. a FF 85mm f5.6 lens and a m43 42.5mm f2.8 lens have the exact same physical aperture of 15.2mm. That's physically what the light is going through (85/5.6=42.5/2.8=15.2). Given the same exposure time, they get the same light. The m43 spreads it over 1/4 the area but it's 4x as intense giving the same total light.

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Apr 29, 2015permalink

Richard Butler

Richard Butler

eddychan008:

85mm F5.6 (FF) and 42.5mm F2.8 (1/4 the size): Same total amount of light.

85mm F2.8 (FF) and 42.5mm F2.8 (1/4 the size): Same light per unit area (which is what F-number, rather than aperture diameter gives you), but with four times the area, so 4x more light.

The fact that it was captured over four times the area becomes irrelevant as soon as you compare the images at the same size.

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Apr 29, 2015*permalink

riman

I dont get why you say its irrelevant that you captured the image over an area four times as large...doesnt that mean the pixles capturing the light are four times as large and therefore the light to noise ratio is four times better??

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May 15, 2015permalink

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rogeriosm

rogeriosm

Great article. Thank you for sharing the knowledge.

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Apr 29, 2015permalink

mediasorcerer

mediasorcerer

My personal feeling is, that with some sensors,[the better quality ones] the noise can actually be pleasant and an artistic asset rather than a detraction depending on how why and where its used.

This really is a great article and just the sort of interesting and useful information many photographers may want and need, although im just some stranger, and already aware of the paradoxical iq juggling act between iso s/p and ap/, im going to politely insist you pat yourselves on the back for taking the time to explain and bring this concept to the readers attention.

I hope you produce more like it.

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Apr 29, 2015permalink

Felipe Rodríguez

Felipe Rodríguez

Agreed! I have recently switched from Canon to Nikon mostly because of what you mention. I noticed that in Nikon images (I mean those taken with full frame Nikon DSLRs), noise was quite pleasant, and randomly distributed in a way that reminded me of that wonderful old photographic film grain; meanwhile, on the other side, my Canon files showed a rather ugly, clearly "digital" noise. So now, after many years of taking care to expose to the right, I am not hesitant of letting the histogram go more to the center (if needed) because the shadow recovery capability in raw Nikon files is, well, simply amazing.

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Apr 29, 2015permalink

mediasorcerer

mediasorcerer

Yes you understand exactly, it sometimes cannot be completely eliminated anyway so id rather try to work with it, and frankly, with the ff cam im using atm, i REALLY like it for exactly the same reasons, the natural & organic opaque diffusion & dispersion of random granular can be a huge aesthetically pleasing composite of any given image.

and full frame sensors are where it seems to really shine, the ff one im using anyway, i fully agree ive seen it in nikon files too coincidentally. Not so much in Canon but it may be there.

Yes the recovery is amazing i agree, i say that from personal experience.I used to bracket either side but now i bias to darker myself for exactly the same reason, and i love dark moody images, that reminds me of film too lol/

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Apr 29, 2015permalink

solsang

solsang

Mostly chroma noise is ugly while grainy b/w noise tolerable, and good sensors do make very nice grain noise - some photo apps even have a setting for applying grain to the image to make it better:)

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Apr 29, 2015permalink

Jos G

I fully agree and think that sometimes the argument for selling cameras with lower noise is comparable to the megapixel-race.

I still shoot a lot with the Olympus E-3 for the reason that it's noise at ISO 1600 (in b/w) has a similar effect as the good old Tri-X had: very contrasty, sharp black lines and an apparent but not distracting noise over the image. I love it. (as much as I dislike color-noise, but that's where the Nikon D700 and the likes come in action).

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May 10, 2015permalink

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mediasorcerer

mediasorcerer

Great article and thank you, so i presume that smaller sensor equals lower image signal noise quality , because the signal to noise ratio is lower with larger light gathering surface area?

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Apr 29, 2015permalink

Wiscflank

I like the explanation of shot noise. Very interesting. However, the connection to the sensor size rather than the pixels size is not obvious. Everything holds together, but the conclusion. Smaller sensors are noisier, but if we agree on the fact that the pixels are independent from one another, meaning the light received by one photocell does no impact its neighbors, the logical conclusion is to state that the size of the pixels is important, not the size of the whole sensor.

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Apr 29, 2015permalink

Richard Butler

Richard Butler

My understanding is that, precisely because the shot noise is uncorrelated between pixels, the SNR of one large pixel can be recreated by combining the results from any number of smaller pixels that cover the same area (ignoring, for now, read noise, which I'll cover in part 2).

At this point, if you make the (I think) reasonable assumption that people don't choose their viewing or print size based on the sensor format or pixel count it was captured on, then high pixel-count images will be downsampled to the same size as low pixel-count ones, with no difference in shot noise between the two.

At which point it's the total amount of light making up the image that matters most, and this is where the size of the sensor can enter into play.

As I say, there'll be a more rigorous look at this in part 2.

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Apr 29, 2015*permalink

Jos G

I might be wrong about this, but cameras like the Nikon D800 with pixels the size of those found in the Olympus E-3, have less noise because the total number of pixels is larger and thus it captures more photons and the amount of random pixels is larger. If you would only use 1/4th of the sensor, than you 're right, but in the comparison to the rain an buckets, you just place more smaller buckets, so your chance to capture more raindrops is bigger. On the other hand, the sensor of the Nikon D700 has larger (the largest) pixels, comparable to wider buckets and has a very low noise ratio because even so the chance to capture light is bigger.

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May 10, 2015permalink

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riman

I just tested this idea and it seems to work...Here are two shots both at 11,000 ISO one was overexposed two f stops and the other underexposed by two...and it really makes a difference!

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Apr 29, 2015permalink

Jos G

I have done the test a few years ago with the Olympus XZ-1 (RAW) by applying the same exposure at ISO 100 as required to ISO 800 and compared the images while the ISO 100 shot was heavily tweaked and that one showed a much more acceptable image than the one at ISO 800.

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May 10, 2015permalink

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riman

I do believe this is a true statement of what is happening as I have seen a huge amount of noise in underexposed shots at very low ISO

So can you just go to the answer section in the back of the book and tell us,,,if we want less noise in our shots should we shoot raw and add an additional F stop of exposure..half stop or what? or is this something we should do only in low light situations?

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Apr 29, 2015*permalink

Karroly

Are you lazy ? ;-)

The answer is at your reach : just try ! It is safe...

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Apr 29, 2015*permalink

riman

Yes in fact I am quite lazy ,,,but i moved my butt and did the experiment and it is true..Now i have to rest..not used to such heavy work..

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Apr 29, 2015*permalink

Karroly

I am happy you tried it for me. I am lazy too... ;-)

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Apr 29, 2015*permalink

riman

Honestly i found that underexposing results in lots of noise when corrected but I cant honestly say there is a big difference when I overexpose..seems about the same as when using "correct" exposure... I was hoping for something more...

Maybe I am missing something? One guy told me he overexposed by one third of a stop...how can that make any difference?

I think we need more clarity here..if there is a way to significantly reduce noise without using Noise reduction software...i would like to know it

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Apr 29, 2015permalink

Jos G

@riman: overexposing a sensor is never a good idea, just as it was! What is gone, is gone!

The trick to have as less noise as possible with your sensor, is to expose as bright as possible without clipping (overexposing) important parts in your image. Therefore you can use the histogram, but very useful is the overexposure warning of your DSLR: check for blinking parts and correct the settings by 1/3 (if possible and necessary). You will guess this method only applies when not shooting action or candid photo's!

I still might warn that setting your goal to the technical perfect photo, might ruin the pleasure of looking at a moment in time that will never ever return...

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May 10, 2015permalink

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Prairie Pal

My thanks to the author. Very well paced and clearly explained.

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Apr 28, 2015permalink

Ron Poelman

Ron Poelman

ETTR ?

Well trolled, DPR.

Since when is noise the primary reason for selecting exposure level ?

Aesthetic considerations have nothing to do with exposure, right ?

Just get the noise right and it's a masterpiece every time.

Bizarre.

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Apr 28, 2015*permalink

Great Bustard

One seeks to maximize the amount of light on the sensor to minimize noise (and maximize DR) within the constraints of blown highlights, motion blur, and DOF. Depending on the relative amounts of each and the aesthetics of the photographer, different photographers may choose a different

If the article said otherwise, that oversight should be corrected.

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Apr 28, 2015permalink

Rishi Sanyal

Rishi Sanyal

Epic troll of DPR, mate ;)

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Apr 29, 2015permalink

SmilerGrogan

No, he's not trolling. He's pointing out that ETTR and this whole theory of exposure you guys are trying to push is a case of the tail wagging the dog. Why? Because you are inviting people to worry about extraneous details that decades of innovation in imaging science have basically taken out of the equation.

Part of the DPR problem in understanding other viewpoints stems from the overcast up there and in DPR's roots in the UK (same goes for Canada-based Luminous Landscape); you guys live in a low-contrast lighting environment where it's OK to expose for highlights because the gentle falloff you are blessed with. The rest of us live in a world of extreme contrast where it's easy to blow channels in a way that is impossible to recover.

Think about switching to a subject-oriented style of metering; teach people to identify the subject of the photo, then meter so that the brightness value of the subject is where it needs to be for the composition rather than trying to find it in post

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Apr 29, 2015permalink

ottonis

@Ron Poelman

In case you haven't noticed, this DPR article is about NOISE!!

And yes, ETTR is a means for getting quite a few things right, including but not limited to SNR.

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Apr 29, 2015permalink

Rishi Sanyal

Rishi Sanyal

'decades of innovation in imaging science' haven't taken out the basic principle that collecting less light=more noise, which is what we're stressing. There's this huge misconception amongst some that it's your camera's ISO setting & electronics that cause the noise at higher ISOs. We're pointing out that the biggest factor is the amount of light you collect.

We're then pointing out that when you have the option of optimizing your exposure, & you might care about noise levels in your image, then your best bet will be to use ETTR philosophy, which advocates giving your camera as much exposure as possible just short of clipping tones you don't want clipped.

Ironically, ETTR is exactly for the high contrast scenes you mention, & it's pretty disingenuous of you to say up here in Seattle we just shoot grey images... considering the high DR sunset images we've been posting of late!

ETTR ensures you've not blown highlights, but have minimized noise in shadows you may wish to push later.

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May 1, 2015permalink

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Tonio Loewald

It seems to me that "shoot to the right" was more useful in the film era — film has ludicrous (almost infinite) over-exposure latitude (it's not practical to recover it without some kind of high tech enlarger, but I read somewhere it's in the neighborhood of 22-stops). These days, certainly at lower ISOs, it's often advisable to somewhat under-expose lest you accidentally blow out small highlights that aren't apparent in your histogram.

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Apr 28, 2015*permalink

Rishi Sanyal

Rishi Sanyal

Exactly. And that's actually a hallmark of ETTR, though the term itself may be a bit of a source of confusion. ETTR only posits that you should l give the camera as much exposure as you can just short of clipping any important scene element at the level of the sensor. Not more.

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Apr 29, 2015permalink

Just Ed

Just Ed

Tonio, "enlargers" are decidedly low tek. It is uo to the photographer doing the shooting and printing to control/manipulate the exposure and develop the image properly for the best tonality. Its one heck of a lot more work than digital.

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Apr 29, 2015permalink

Tonio Loewald

The problem with ETTR is that looking at a histogram on a small LCD is often misleading and you won't realize you've blown a highlight. Indeed, I prefer to slightly underexpose in a lot of cases (and I'm hardly alone in this -- e.g. "Expose to the right is a bunch of bull" http://theonlinephotographer.typepad.com/the_online_photographer/2011/10/expose-to-the-right-is-a-bunch-of-bull.html).

Yes, it's great if you *know* you're not clipping, but many of the most interesting photographs feature huge dynamic range and you can't get those blown highlights back — you can clean up noise in deep shadow.

If the hump of your histogram is on the right then the chances are VERY high you have blown highlights, even if you don't see a spike in the histogram.

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May 1, 2015*permalink

Jos G

Indeed 'negative' film could endure a few stops of overexposure, but doing so with positive film, would have the same result as overexposing your sensor these days!

To prove the similarity or equality (to myself) between positive film and my DSLR's sensor, I examined my slides with dark shadows and found these also have more graininess in those areas.And don't think of slides as miracles: 22 stops is huge, even for the best slides. Not even human eye can capture that much information (slides can do 5-6 EV and the highest range belongs to the best developed best black-and-white negative films which cover about 13-14 EV, not even comparable to the Nikon D800 (14.4EV). If you would like the resolution of the Nikon, you would have to use a heavy Medium Format with an expensive lens and do not compare those to the modern medium format sensors... times have changed. In my opinion, the digital sensors have clearly won over film, but that's the technical quality of course!

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May 10, 2015permalink

Jos G

@Tonio Loewald: you are right, there is a lot of bull* in the comments to ETTR. The histogram and the over-exposure warning are sometimes inaccurate or inadequate. But: learning to read the display you have with you at the moment and comparing the readout to what your monitor says when you get home, is a lesson you should never skip!

Spend time learning when your camera display is still right (or wrong) and more important: using your camera's metering system and how accurate it is in telling you when your image will be overexposed, is rewarding. Especially the spot-meter, that is.

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May 10, 2015*permalink

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Ben Stonewall

I thought all the noise just came from whiney fanboys ;-)

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Apr 28, 2015permalink

Sangster

Would using a bigger light gathering lens to concentrate the photons onto the sensor reduce noise, ceteris paribus?

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Apr 28, 2015*permalink

Tonio Loewald

Yes, but — consider an individual sensel (one pixel sensor). In a smaller sensor either you have fewer pixels OR smaller pixels. By and large you have smaller pixels, right? So if you concentrate a given amount of light onto the smaller sensor you'll be spreading it over more sensels.

The absolute light gathering power of a lens is determined by its aperture relative to the image circle (f2 -> 1/2 the image circle). So the kind of lens you're talking about would be something like an f0.25 lens, which is unheard of because it would be so optically challenging.

Now there's at least one company that uses multiple lenses and multiple sensors to achieve something like this kind of thing — it was just bought by Apple.

http://tinyurl.com/odv43cn (WSJ)

Incidentally, this technique (multiple lenses with multiple sensors) has been used by astronomers to create virtual enormous aperture telescopes for quite some time.

http://en.wikipedia.org/wiki/Telescope_Array_Project

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Apr 28, 2015permalink

ottonis

That's exactly what "speed boosters"do: they "concentrate" the light from a larger FF lens to the smaller area of the APSC sensor.

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Apr 29, 2015permalink

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cysunza

cysunza

Great article! even I knew this and I apply this to my every day work, it's a very good technical explanation that helps a lot to me in my roll as a photography teacher, so thanks a lot.

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Apr 28, 2015permalink

Unsubscribe me please

Unsubscribe me please

Thank you Richard Butler for a very, very, good and understandable explanation of Shot Noise.

I like the metaphor you chose.

I was on a project many years ago where the project leader explained the physical limitations of sensors. In his case, he chose Neutrinos as the random material.

Your use of Rain drops as an example of randomness is far better as it’s something we can all see!

Thank you for shedding more good light on this subject whereby my brain doesn’t have to amplify the information too much to understand it.

In future, I will now think more to the right.

Kind Regards, … Barry M Australia

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Apr 28, 2015permalink

Mike FL

" it means using the brightest exposure you can possibly get away with".

For the same EV and ISO, is there any difference between "fast aperture with fast shutter speed" and "slower aperture with slower shutter speed" in terms of noise?

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Apr 28, 2015*permalink

Olymore

Olymore

My understanding is that it shouldn't make any difference as far as noise is concerned if the total amount of light is the same.

Shot noise relates to the behaviour of photons at the quantum level and if the total number of captured photons is the same the shot noise should also be the same.

Of course there are other considerations like DOF, subject movement that may influence the decisions you make when setting those parameters.

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Apr 29, 2015permalink

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Karroly

You forget to say that increasing the diameter of the "tubes" is like waiting longer under the rain : this will increase and make more equal the number of raindrops caught by each tube, thus reducing the "signal-to-noise" ratio. For sensors, it means, putting aside electronic noise, bigger pixels will catch more photons and average the random nature of light you are talking about here.

This is why, given the same resolution, a big sensor with big pixels will ALWAYS be better in (extremely ?) low light than a small sensor, even though there were no electronic (or thermal) noise at all...

However, in practice, the true question is, and your article does not give an answer, under which pixel size and scene brightness, does a pixel catch too few photons so that the difference between adjacent pixels becomes noticable ?

Is this "noise" greater or smaller than the electronic or thermal noise ?

In other terms, do we really have to care with the random nature of photons with today sensors ?

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Apr 28, 2015permalink

Richard Butler

Richard Butler

Using a larger test tube is just like adding together all the water collected in the smaller tubes. From a shot noise point of view there's no difference.

There is a read noise difference, but that's the topic of part 2, which is why it's not covered here.

Exactly when you're limited by shot noise and when you're limited by read noise will vary, situation to situation and camera to camera, but again, that's something for part 2.

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Apr 28, 2015*permalink

digiart

"But there are more of the smaller pixels, so they can be combined, thus negating the big pixel advantage as long as the noise is scaled adequately."

If pixels where combined, that would negate the advantage of increased pixel count as it would decrease resolution.

Also, each pixel is amplified individually in the sensor and it's this first amplification step that contributes the most to the sensors SNR. So, "combining" smaller pixels will always result in lower SNR than using a sensor with less but bigger pixels, assuming sensors are of same generation (same type, process).

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Apr 28, 2015permalink

Karroly

@HumanTarget,

"I think you mean increasing the signal-to-noise ratio?"

Yes, you are right.

"But there are more of the smaller pixels, so they can be combined,..."

No, you are wrong because you do not compare apple with apple. And the apple here is resolution. My hypothesis was : "given the SAME RESOLUTION, a big sensor with big pixels..."

So combining pixels with the small sensor will decrease the resolution compared to the big sensor... And comparing the noise level of two pictures that do not have the same resolution, in other words the same level of details is just nonsense.

@ Richard Butler,

"Using a larger test tube is just like adding together all the water collected in the smaller tubes. From a shot noise point of view there's no difference."

You are right if we compare two sensors of the same size with a different pixel count and thus a different resolution. But this is not my hypothesis here...

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Apr 30, 2015permalink

Karroly

@ HumanTarget,

Whatever the size of sensor A and sensor B, if they have the same resolution, then combining pixels with sensor B will produce a lower resolution picture than sensor A uncombined. Is it that hard to understand ?

"Do you always view/print images in proportion to their resolution?"

I have never said that the print must me done proportional to their resolution. I said exactly the opposite : at the same elargement (that is to say paper size).

"You never resize images for a particular output?"

And what is an enlargement if not a resize for a particular output ?

So please, before commenting, read carefully...and think

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Apr 30, 2015*permalink

Karroly

@ HumanTarget,

I exactly said this "And comparing the noise level of two pictures that do not have the same resolution, in other words the same level of details is just nonsense."

You have to carefully read every word, please...

If the result of such a comparison shows that picture A with the low resolution has less noise than picture B with the high resolution what can you concluse ? Which camera is better in low light ? You cannot tell it... This is exactly why I say it is nonsense. You have to change your comparison protocol.

You have to downsample (and not downsize) the picture B down to the detail level of picture A to tell it.... And the downsampled picture may then be less noisy than picture A... or not ! But finally you will know which camera to take to shoot in low light as long as the resolution of camera A is enough for you.

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May 1, 2015permalink

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Mssimo

Mssimo

In a few cameras with "ISO Irreverence". Would you recommend not to use anything but base ISO up to the point where the camera starts to use hardware amplification?

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Apr 28, 2015permalink

Richard Butler

Richard Butler

I like ISO Irreverence, I might have to use that.

That's a subject for part two. Which I need to finish writing and illustrating.

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Apr 28, 2015permalink

mpgxsvcd

Stop chatting and keep writing. :)

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Apr 28, 2015*permalink

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VidJa

does anyone know where we are in efficiency of the sensors? with other words, how many of the available photons do we measure with current sensors and how far can we expect to improve?

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Apr 28, 2015permalink

martindpr

I guess about 1/10.000 of the available light, or 0.01% efficiency, read my comment bellow on graphene.

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Apr 28, 2015permalink

SimenO1

martin, your have got your numbers very very wrong.

QE of a modern FF CMOS sensor without color filter array can reach about 90%. The color filters are intentionally not blocking out the two other colors completely. Its actually blocking about 50% of the light. Transmission losses in the lens is about 10-30%, where the 30% number accounts for sub optimal light angle and reflections in the filter stack or in the sensor it self (assuming FSI type sensor). The loss of electrons on the chip, between the well and the ADC is actually very low. From a few percent in worst case to less then a percent in best case.

For comparison 70-style color film makes use of only about 2% of the light hitting it.

Another comparison: Commercial cheap multi crystalline solar cells have an efficiency of about 10-25%.

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Apr 28, 2015*permalink

Great Bustard

@martindpr:

As SimenO1 correctly points out, you are way, way, way off.

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Apr 28, 2015permalink

mike703

the information you want is here. Efficiencies are now up to 80-90% in the best cases

http://www.sensorgen.info/

Best wishes

Mike

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Apr 29, 2015permalink

martindpr

Nikon D2X 476%, mhm, yeah right... If 100% is max efficiency, then D2X must be inventing more of it according to the source you posted.. Read this article: http://www.gizmag.com/graphene-imaging-sensor/27718/

Stating that: NTU claims it has proved to be 1,000 times more sensitive to light than existing complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) camera sensors in addition to operating at much lower voltages, consequently using 10 times less energy".

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Apr 29, 2015permalink

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Karroly

"As a result, when you shoot two different sized sensors with the same shutter speed, f-number and ISO, the camera with the smaller sensor has to produce the same final image brightness.. from less total light."

I am sorry, I do not agree at all.

Please, let me put this another way. If I use an F:2.8 FF lens on a APS-C body, it is still an F:2.8 lens and the picture taken (at same aperture/speed/ISO AND PIXEL SIZE) is just a crop of the FF sensor. The APS-C area of the FF sensor gets the same amount of light (either total or per area unit) than the APS-C sensor and thus the signal-to-noise ratio is the same...

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Apr 28, 2015permalink

Richard Butler

Richard Butler

You may not agree, but it remains true, I'm afraid.

You're right that the APS-C crop from the full-frame camera will be identical to the native APS-C image (same light per unit area, same area). It's also the case that the pixel-level quality will be the same because the light per unit area is the same.

However, as soon as you view all three images at the same size (either by blowing-up the APS-C crops or downscaling the full frame image), the full frame image will be cleaner.

The full frame image is made up from more signal, and this grows faster than noise. There'll be more of a discussion of this in part two (or possibly three) when we look at the effect of combining data from multiple pixels.

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Apr 28, 2015permalink

Richard Butler

Richard Butler

For a rough example, compare the Nikon D7000 to the D800

The APS-C region of the D800's sensor is around 15MP, rather than the D7000's 16MP, but it's pretty close. In this example both are shot at f/5.6, 1/640 seconds.

At native resolution you can see that the pixel-level performance is very similar (as theory would suggest).

Now click on the 'Print' button at the top right of the widget, so that you can compare them at the same scale. The camera that's captured more signal looks better, even though the pixel-level performance was very similar.

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Apr 28, 2015permalink

mpgxsvcd

Except for the fact that the A-PSC sized sensor didn’t use all of the light that passed through the front element of the lens. It is true that each pixel still receives the same amount of signal. However, the signal to noise ratio is lower since some of the signal got thrown away and yet the shot noise is still the same.

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Apr 28, 2015permalink

Karroly

@ Richard Butler,

This was just a misunderstanding. I made the comparison at pixel-level, a rather "technical" approach (I am an engineer before being a photographer, you know...) when you make the comparison at the same enlargment size, which I did not catch at first : this is the photographer (and right) approach.. ;-) Then, the sensor size matters more than the pixel size.

However, as sensors are not gapless, given the same sensor size, increasing the pixel size reduces the area used by gaps and increases the active area of the sensor and its ability to collect more photons. This should produce a cleaner image for the same print size. Is it something that you have observed ?

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Apr 28, 2015permalink

Richard Butler

Richard Butler

Karroly - microlens design tends to be very good in terms of minimising the effect of gaps between pixels. Then, for very small pixels, technologies such as back-side illumination (BSI) help maximise the photosensitive area of each pixel.

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Apr 28, 2015permalink

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Marcelobtp

So now i can understand why have a "sun" inside my studio with very high shutter speed; leaf shutter please... Burn the model and get the finnest image quality possible.

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Apr 28, 2015permalink

Richard Butler

Richard Butler

The very fast shutter will cancel-out the benefits of mounting a star in your studio.

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Apr 28, 2015permalink

Marcelobtp

Can i say that with higher quantity of light i'm cancelling more the ambient light so i'm "purifying" the light and reducing the randomness?

I know to really reduce the randomness in a strict way i would need to speed up the light speed.

But the purity of light does not interfere in this randomness like air friction does with the water?

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Apr 29, 2015permalink

DenniRau

Hi Richard,

Cool article. Learned some and looking forward to part two.

My critique: I dont agree on your view on full-frame f/2.8 vs. four-thirds f/2.8. The full-frame would receive four times the amount of light, but this is spread over four times the area..

Quoting Nasim Mansurov: "So let’s get another fact straight: smaller format lenses have exactly the same light gathering capabilities as larger format lenses at the same f-stop, for their native sensor sizes. Yes, larger aperture diameter lenses do transmit more light, but more light is needed for the larger sensor, because the volume and the spread of light also must be large enough to cover the bigger sensor area."

The noisier images from smaller pixels is better explained by a parallel analogy of test tubes. Smaller tubes covering an equal area would display more variance than larger tubes exposed to the same shower for the same time.

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Apr 30, 2015permalink

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DirkL

Given the same amount of light, a larger sensor will be illuminated less than a smaller sensor.

See the definition of lux.

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Apr 28, 2015permalink

Richard Butler

Richard Butler

That's true, but you'll need to state a lot more of your assumptions for that statement to be photographically meaningful.

The point made in the article is: when trying to take the same photo (same shooting position and framing, ie: equivalent focal lengths), then in the same scene illumination, with the same f-number and shutter speeds, the large sensor will see the same luminous flux per unit area as a smaller one and hence will be more illuminated in total (since it is measuring that flux over a greater area).

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Apr 28, 2015permalink

DirkL

N

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Apr 28, 2015*permalink

Great Bustard

@DirkL

You need to distinguish between the density of light falling on the sensor (exposure, measured in lux · seconds, or, equivalently, photons / mm² for a given luminosity function) and the total amount of light falling on the sensor (lumen · seconds, or, equivalently, photons, again, for a given luminosity function) and understand that, in terms of the visual properties of the resulting photo, it is the latter, not the former, that matters.

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Apr 28, 2015permalink

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pictureone

This is an excellent article about picture noise. After reading , in low light I think it is better to increase EV than increase ISO that will increase noise

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Apr 28, 2015permalink

pidera

Yes and No. Increasing ISO will brighten up the image. Selecting a slower shutter speed (risk : motion blur) or a larger aperture diameter (risk : too shallof DOF) will reduce noise.

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Apr 28, 2015permalink

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pidera

As pointed out by others, the summarizing phrase "There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor." is a bit unambitious. Shutter speed and physical aperture do the trick, no need to bring in sensor size except for the fact that sensor size and available options for physical apertures are somewhat linked (albeit more in the past than now).

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Apr 28, 2015*permalink

Richard Butler

Richard Butler

I agree but it made more sense to me to talk in terms of sensor size (which people can relate to), rather than aperture diameter or equivalent aperture, which some people push back against.

I wanted the largest possible group of people to be able to engage with the article, so I tried to avoid anything that would distract from the main points I was trying to make.

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Apr 28, 2015permalink

pidera

Hi Richard. Yes, I see your point. Thanks for answering !

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Apr 28, 2015permalink

RedDog Steve

RedDog Steve

Richard, I think you succeeded. Very digestible read without being too simplified. Anyone with any "left-brain" at all will have followed easily. Looking forward to part II.

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Apr 29, 2015permalink

mosc

Richard. I think the physical aperture instead of the pairing of sensor size and fstop is the key to helping people understand equivalence. Talking about light passing through an aperture over a given shutter time makes the lens and camera disappear into a black box behind a circular opening. People then much more intuitively understand total light. No matter the sensor or flange distance it's the same resource all that tech is trying to accurately record.

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Apr 29, 2015permalink

NarrBL

Richard, I think you did very, very well in the article -- and in all the clarifying answers to persons who may be visualizing differently. Credit where due also to Rishi, and Karroly with others considering carefully. Ready now for the 'ISO irreverence' ;)

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Apr 30, 2015permalink

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duartix

4 pages of article could be summed up in 4 letters: ETTR.

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Apr 28, 2015permalink

pidera

It also says that lack of light is the largest source of noise. And not the sensor. A point for making equivalent iso cross format comparisons instead of same iso cross format comparisons. Still waiting for that Widget ;-)

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Apr 28, 2015permalink

NarrBL

I suspect that for actual photography, it will turn out a little more subtle than that...

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Apr 30, 2015permalink

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Everythingis1

Everythingis1

This right here is how you become the anandtech of photography! Excellent presentation, keep up the great work!

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Apr 28, 2015permalink

Terry Breedlove

Terry Breedlove

Just like in the film days. Bigger format equals more image quality. Smaller format gives up some image quality for better mobility. Choose what you need and want for what you like to shoot.

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Apr 28, 2015permalink

pidera

Yes and No. Bigger format gives more options to choose from in terms of image quality. For many situations results overlap.

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Apr 28, 2015permalink

obsolescence

obsolescence

Bigger format gives shallower depth of field for any given aperture and lens field of view. Anyone who has shot 8x10" film knows that stopping way down is essential for most scenes. That requires much longer exposures which is limiting. I forget the exact amount, but it's something like 8 stops compared to 35mm film.

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Apr 29, 2015permalink

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snapster

Great article Rishi. All of the comments and your responses to many of them enhance the article. Looking forward to parts 2 and 3

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Apr 28, 2015permalink

TrojMacReady

TrojMacReady

Thanks for the well written article.

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Apr 28, 2015permalink

(unknown member)

Very nicely written article that explains a somewhat complicated subject in a way that makes it easy to understand with the help of suitable analogies and an elegant way of putting this into easy to read text. Appreciate the hard work you guys put into the articles of this site.

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Apr 28, 2015permalink

mpgxsvcd

In order to believe this article you have to accept that shot noise is a significant factor in short exposure photography. That fact is stated in the article. However, it really isn’t demonstrated. I think that is where some people are getting hung up. They can’t accept that fact without seeing it.

It would be really cool if you showed how much noise is contributed from shot noise vs. read noise in each review. You could stack out the read noise with Dark Frames leaving only the shot noise from a very dark scene.

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Apr 28, 2015permalink

mike703

You can calculate it easily enough from here:

http://www.sensorgen.info/

Take the first on the list (EOS 1000D). Full well capacity of 34000 electrons so at base ISO the shot noise associated with the brightest parts of the pic will be sqrt(34000) which is around 185 e. Read noise is given as 5 electrons. So Read noise is less than 3% of shot noise if you expose to the right at base ISO.

For an EOS-1DX, shot noise in the highights at base ISO is sqrt(90000) = 300 electrons. Read noise is 1.2e, so is <1% of shot noise.

Going back to the 1000D, to have read noise (5e) equal to shot noise, you'd have to have a maximum signal of 25 e (instead of 34000!) as the brightest part of the picture - which is equivalent to an ISO of over 100,000...

Best wishes

Mike

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Apr 28, 2015permalink

mpgxsvcd

Very good information there Mike. Thanks for that.

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Apr 28, 2015permalink

Sudo Nimh

@mike703, why is shot noise equal to the square root of the number of photons? Do you mean it is proportionate to the square root?

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Apr 29, 2015permalink

Report

mike703

No, it is *equal* to the square root: a consequence of normal statistical sampling - see

http://en.wikipedia.org/wiki/Shot_noise

(paragraph 6, beginning 'for large numbers...)

To use the test-tube analogy from the article, let's say the density of raindrops and width of the test tube mouth means that the average number of drops collected per test tube is 100. So if you count them all and plot a distribution curve, it will look like a bell curve with a standard deviation of +/- 10 raindrops.

This arises because the random distribution of raindrops does not mean that they fall exactly evenly, everywhere - that is definitely not random. (Get 100 blindfolded people to lob a dart at a dartboard so that the board has 100 randomly-distributed holes in it. Are the holes perfectly evenly spread out with the same number in every square inch? Or will there be some clumps of holes close together and some areas with no holes?)

Best wishes

Mike

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Apr 29, 2015permalink

SmilerGrogan

Is there a way to use the inter-ocular method of analyzing this table? For instance, it looks to me that like the Canon S120 point-and-shoot has the lowest noise versus best QE. Would that be correct?

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Apr 29, 2015permalink

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sans culotte

As in mentioned equivalence article here are some important details omitted.

"the full frame camera will see four times as much light as a camera with a Four Thirds sensor"

The camera itself doesn't deal with light. Light is recorded by sensor pixels. So pixel density & efficiency is the key.

FF sensor area is 864 mm^2 & APS-C sensor area is 329 mm^2. That means Fuji 16MP sensor has lower pixel density (16000000/329 = 48632 px/mm^2) than new Canon (or Sony, who knows?) 50MP sensor (50000000/864 = 57870 px/mm^2). So in this example with FF you get more detail with relatively same noise, it's still nice, but easily shows that bigger sensor doesn't automatically means more light.

Also there is sensor efficiency which has an impact on final result.

All that means that the only reasonable way is comparing specific sensors noise rate.

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Apr 28, 2015*permalink

BeaverTerror

BeaverTerror

When you downsize the 50MP full frame image down to the same dimensions as the 16MP APS-C image, the full frame image will have superior noise characteristics.

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Apr 28, 2015permalink

talmy

talmy

Yes, the article should be talking about the pixel density. It really the light per pixel that determines the noise and not the sensor size. In the analogy given in the article, making the test tubes bigger will reduce the variations in water among the tubes.

Downsampling (downsizing) an image has the same effect as making the pixels bigger, so reduces the noise. Now if you just cropped the 50MP image to one that was 16MP, the noise would be the same, naturally, because the pixels are untouched.

Of course it is safe to assume that preparing an image for presentation, they would be resampled to the same size, making FX a "win" for noise over smaller formats. This is obvious in practice, at least from my experience.

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Apr 28, 2015*permalink

Richard Butler

Richard Butler

Because the effect of smaller pixels involves read noise, it's something we'll either look at in part 2 (which is about read noise), or part 3, if we end up extending the whole thing in response to the range of interesting examples raised in the comments.

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Apr 28, 2015permalink

Great Bustard

As Richard Butler noted, the effect of pixel count with regards to noise has to do with the electronic noise. If, for example, a 1x1 pixel had the same electronic noise as a 2x2 pixel, then a sensor made from 1x1 pixels would have twice the electronic noise as a sensor of the same size made with 2x2 pixels.

If, on the other hand, a 1x1 pixel had half the electronic noise as a 2x2 pixel, then the total electronic noise would be the same.

If the 1x1 pixel had less than half the electronic noise of a 2x2 pixel, then the sensor with more smaller pixels would have less electronic noise.

In any case, the electronic noise is only relevant for the portions of the photo made with very little light (deep shadows at base ISO, and progressively more of the photo as the ISO rises, typically becoming an issue by around ISO 3200 in modern sensors).

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Apr 28, 2015permalink

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GoneMirrorless

I have found that over sharpening is of often confused with noise, especially in combination with slightly out of focus images.

It has little to do with this article, but I see people who did everything correct to avoid noise, then sharpen the heck out of the image, and complain it looks too 'noisy'.

Most here know the difference though.

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Apr 28, 2015permalink

mpgxsvcd

“There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor.”

I am confused about the statement above. The aperture diameter determines how much light is available to your sensor, right? The focal ratio just determines how concentrated that light is. The focal ratio does not affect the total amount of light that is available at all. The aperture diameter does that.

The focal ratio only affects the light per unit area. However, your statement refers to total light available. Or am I reading that wrong?

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Apr 28, 2015*permalink

mpgxsvcd

“when you shoot two different sized sensors with the same shutter speed, f-number and ISO, the camera with the smaller sensor has to produce the same final image brightness (which the ISO standard demands) from less total light.”

I guess where I was getting confused was that you didn’t specify that the focal lengths were the same in the above statement. The shutter speed, f-number, and ISO could all be the same but if the focal length for the m43 sensor was half that of the full frame sensor then both would be seeing the same total light because the aperture diameters would be the same.

Should the statement above also say that the focal lengths or aperture diameters are the same as well? If either one of those is different then the sensors could see the same amount of light despite their size difference.

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Apr 28, 2015permalink

mpgxsvcd

I see where my mistake is now. You were implying that the lens was identical in both situations so the total light and the shot noise through the lens was equal in both situations. However, the smaller sensor literally discards a portion of that light because that light falls outside of its area.

When looking at it like that then yes the sensor size is what causes the light loss and therefore would decrease the signal to noise ratio.

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Apr 28, 2015permalink

zodiacfml

f-number more accurately determines light received as this value also includes the distance in contrast to the aperture.

light gets weaker with longer distances, including any length of a lens. this is also the reason why it is rare and expensive for longer focal lengths to have fast f-numbers.

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Apr 28, 2015permalink

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Chris2210

Chris2210

I was expecting this article to have at least some explanation of why pixel pitch is important - particularly at high sensitivities. It's fairly straightforward by my understanding:

To follow the test tube analogy in the scenario of a very low sample [rain or light whether that's short exposure or low flow] a larger test tube/ sensel gives a better chance of a sample which is useful. Greater numerical arrays [be that tubes or megapixels] may be able to reduce the effect of noise by averaging out across neighbouring captures [downsampling], but once the individual samples become increasingly unreliable that no longer applies.

Hence sensors at any given size with larger/fewer receptors will have a potentially higher sensitivity ceiling [all other things being equal]. That's right, isn't it?

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Apr 28, 2015permalink

mike703

Imagine taking a 10MP sensor and then subdividing it into a 40MP sensor; 4 small photosites cover the area of one large one.

The large photosite can count 4x more photons, so the uncertainty (noise) is halved compared to a smaller photosite. But with the smaller photosites, you have four of them in the same area. Each individual one is 2x noisier, but if you average the readings from four over the same area, the noise goes down by the square root of sample size –it is halved. The result is a draw, for a given sensor area: it makes no different how many photosites you split the sensor into, the noise per unit area of sensor, or per unit area of final print, is the same. So total noise basically relates to sensor area, not MP count.

To put it another way: the smaller photosites are individually noisier, but they are printed smaller with more of them per square inch of print so the noise is less apparent – it’s a draw. (But you will get more detail).

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Apr 28, 2015permalink

Chris2210

Chris2210

But if you take the analogy of the test tube again and extend that to a basketball hoop. Put the four hoops together and make the balls small enough to fit in each. Would you get as many scores in four small hoops as the one large? Even if the hoops were square and not round and placed together, you are still going to lose more of your hits to rim-shots - and the smaller the hoop and lower the flow, the more statistically important this becomes.

Where you're getting plenty of data that doesn't matter as much as the overall area covered [so it is overall area rather than photosite which is important overall].

But look at the high end cameras from the big 2 [and Sony] and the cameras which achieve the highest sensitivity ceilings have fewer sensels. I suppose you cold argue that this is read-out efficiency and it can [and is] improved by arrangement improvements, but nonetheless there is an inherent effect of the size of the photosites on absolute sensitivity ceilings.

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Apr 29, 2015*permalink

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SwissRapha

HowaboutRAW, I think you are wrong here. Besides light transmission (T-stop), the lens does not impact the shot noise. How could it?

A better lens can not magically improve the shot noise of the incident light. Similarly, a bad lens (with the same T-stop) does not add shot noise.

BTW, what do you mean with a 'better lens'?

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Apr 28, 2015permalink

SwissRapha

Sorry, double post due to internet connection problems...

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Apr 28, 2015permalink

HowaboutRAW

Swiss,

Better lenses handle light, and color, better.

And the better high ISO results are easy to see. (You can do your own testing. No need to believe me.)

Yes, a not great lens will add noise, because it's not clearly transmitting the light to the sensor or film. Again easy to see.

Recently I happen to have redone this exact test with the Canon 1DX at ISO 25600 in bad lighting with a Canon L and a basic Zeiss MF lens, the difference was astounding.

I more than suspect it's because engineers at Zeiss, Leica, Samsung and Olympus know something about light not in standard textbooks. Fuji and Sigma clearly have some this worked out too.

Nikon finally seems to be learning.

It's also pretty clear (no pun) that binocular companies like Swarovski and Meopta have this worked out too. And even the inexpensive Chinese made binoculars have it.

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Apr 28, 2015*permalink

zos xavius

The "astounding" difference is merely the difference in tstops. A lens does not increase noise on any way. If they are both transmitting the same amount of light, shot noise will be identical.

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Apr 28, 2015permalink

HowaboutRAW

zos,

Gee, you have access to my raws? Not.

Better lenses transmit light better, it is easy to see. And this fact has a significant effect on higher ISO work.

wider apertures could also help, but that's far from all that's going on.

Instead of making claims, I suggest you do testing. I have. And I have significant field experience with this.

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Apr 28, 2015permalink

mikeoregon

mikeoregon

Could you post those image files to illustrate...?

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Apr 28, 2015permalink

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DFPanno

DFPanno

Great article.

I highly recommend Bob DiNatale's book "Obtaining the Optimum Digital Exposure".

Required reading for those that want to produce the most "filmic" files.

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Apr 28, 2015permalink

EcoR1

Here are most important things to understand:

1. Shot noise is square root of the total amount of captured photons. Thus when amount of captured light decreases the shot noise portion of the total signal increases.

2. When ISO-number is doubled the amount of light that one pixel can deliver to the final image will be halved. For example if full well capacity of the pixel is 100 000 photons for ISO-100 it will be 50 000 photons for ISO-200, 25 000 photons for ISO-400 and so on.

3. Combine the understanding from points 1 and 2. Increased ISO will gradually weaken the maximum signal to noise-ratio and reason is decreased amount of light that can be recorded. The reason to increase is ISO is typically lower read noise, but this is greatly dependent of the used sensor-technology.

4. As the shot noise comes from fundamental physics, there can't ever be noise free pictures. Noise will be always present, but one can fight against it by capturing more light, one way or another.

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Apr 28, 2015*permalink

martindpr

Most important thing is the type of those test tubes you got there/their efficiency. Cause 2day with our tech and translated in layman's terms, they have a small opening, bad angle towards the rain and those raindrops evaporate too soon too early before reaching the bottom and collecting in the sampler. And all manufacturers use this same bad recipe. In more technical terms, the color filter reduces at least 2/3 of light (practically 95%), the CMOS samples only 1/100 of the light transmitted by the filter and rest is reflected out or lost in the process, and then at least 30-40% is lost in the circuitry. Then the jpeg looses additional 80% of the information and we're left with 1/1000 of the light information of the original scene. Solution? Refractive type of color filter and graphene instead CMOS for no visible nose at any sensor size.

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Apr 28, 2015permalink

SwissRapha

I think your numbers are way too pessimistic. I am pretty sure the color filter don't filter 95% of the light, 2/3 seems much more realistic.

And with modern anti-reflective coatings and a modern process, the overall quantum efficiency is quite a bit higher than 50%, I think they are close to 90% for green light nowadays, so waayyy more than your 1/100. And I don't see where another 30-40% should be lost.

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Apr 28, 2015permalink

Chris2210

Chris2210

You don't appear to have read the article or you really are talking about your nose not being visible. Shot noise has absolutely nothing to do with a sensor's efficiency - that will be covered by the 'electronic noise' of the next article. Electronic noise is something which can be improved shot noise is a natural, physical process - and far more significant in overall terms than circuit inefficiency.

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Apr 28, 2015permalink

(unknown member)

Not necessarily. PRNU noise can reduce tonal range in highlights, read noise reduces DR and tonal range in shadows and thermal and dark current noise cause problems on long exposures. All forms of noise have their different effects.

If the SNR is above about 35dB, it's pretty hard to tell the difference. Post processing can make more than 5dB difference, even dropping the AA filter and reducing sharpening can make more difference.

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Apr 28, 2015*permalink

Great Bustard

@martindpr:

I'm afraid you are mistaken. First of all, the differences in the light collecting ability of sensors for a given generation is very small. Secondly, even a perfect sensor that recorded every photon that fell on it would still have noise due to the light itself.

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Apr 28, 2015permalink

martindpr

If graphene is 1000 times more sensitive than CMOS, then the numbers speak for themselves. Further on, the RGB filter passes on to the CMOS only a part of one color which is a part of all spectrum (10% at most of all photons of the spectrum, read more on refraction color filters). And lastly, have you seen a hippo being fed with popcorn? You have to fill his mouth with a lot of those for him to know (his treashold is very high), as opposed to a sparrow that senses only one popcorn. So, environmental noise is far less concern than the sensor inefficiency by a factor of 1.000. The hippo is the CMOS and the sparrow is the graphene. Wait a few years when it goes commercial and see for yourself.

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Apr 28, 2015permalink

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SimenO1

"There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor."

I don't quite like this formulation for two reasons:

1. You forgot to take the amount of light in the scene into account

2. f-number and sensor size should be rephrased to effective aperture area (including lens transmission losses) and field of view. I think this is more informative and describes the reason for why sensor size matters, more directly (larger aperture area for a given field of view)

It should also be noted that sensor sizes don't have a finite scale ranging from 1/3" to full frame. It's an infinite scale, but have some physical limitations (from quantum physics to astro physics) and practical current technological limitations: from about 1/10" to about the diameter of a large wafer. And some economical limitations reducing max size to medium format for DPR readers. (NASA doesn't look for telescope sensors here)

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Apr 28, 2015*permalink

Great Bustard

Actually, a better way to phrase it is to say that the amount of light falling on the sensor is determined by the scene luminance, the aperture diameter of the lens, the transmission of the lens, and the exposure time. The size of the sensor figures into things only for base ISO photography in that larger sensors can absorb more light when using a wider aperture diameter and/or longer exposure time.

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Apr 28, 2015permalink

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tinternaut

tinternaut

With the old 12Mp sensors, used by Olympus from the E-30 onwards, I practiced ETTR pretty much religiously. With the newer 16Mp sensors, it's not so important. Nevertheless, if time allows I still bracket a scene up to f1.7 EV. It's hardly scientific, but can produce a very clean, detailed published image.

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Apr 28, 2015permalink

The Squire

The Squire

I always thought ETTR was a bit of a hack, an urban myth even....

Great article. More please.

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Apr 28, 2015permalink

(unknown member)

One big problem with ETTR - channel clipping. The histogram may tell you when the JPEG is clipping, but it usually uses the green channel. If you have a three-colour histogram, it's easier.

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Apr 28, 2015permalink

Jon555

Also histograms are pretty much always made from the JPEG data rather than the Raw, so you have to factor that in too...

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Apr 28, 2015permalink

(unknown member)

Which makes it all a bit haphazard IMO. You can easily blow the red or blue channel without realising it unless you allow for a fudge factor.

I seldom push the highlights up against the stop - you always find parts of the clouds are blown. I normally back off at least 1EV from the clip point, if not more.

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Apr 28, 2015permalink

(unknown member)

>>Which makes it all a bit haphazard IMO.

Really? How did you (or did you) expose film properly without a Histogram. The fact is, the Histogram lies if you're capturing raw data, it's based on the JPEG.

Further, ETTR is all about OPTIMAL exposure. If you don't care you're under exposing and adding noise, do so. But that's not how classical photographers were trained to handle exposure. ETTR is an old word or term that should be replaced with "Optimal" exposure. It's nothing more than that.

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Apr 29, 2015permalink

Iliah Borg

> If you have a three-colour histogram, it's easier

No, it is not - as the green channel normally clips the first.

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Apr 29, 2015permalink

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bwana4swahili

bwana4swahili

"once captured, the signal-to-noise ratio of any tone can't be improved upon." Maybe for a particular image but stacking multiple images of the same scene can improve the signal-to-noise ratio (SNR) by the SqRt of the # of images, i.e.: stacking 4 images will give a 2x improvement in SNR. This approach is very effective and used extensively in low light situations such as astro/nightscape photography.

bwa

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Apr 28, 2015permalink

Great Bustard

Correct. Stacking four photos results in the same amount of light as a single exposure with 4x the exposure time. As a side, many sensors have less electronic noise at higher ISO settings ("non-isoless" sensors, such as Canon sensors), so, for example, stacking four photos at, say, 1/40 ISO 1600 will have less noise than a single exposure at 1/10 ISO 400.

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Apr 28, 2015permalink

Rishi Sanyal

Rishi Sanyal

What Great Bustard said is a good way of looking at it: you essentially end up 'sampling' as much light from n exposures as having shot a n times longer exposure. Except a n times longer exposure may have clipped highlights due to limited pixel capacities, whereas averaging n shorter exposures may not have (since each individual shorter exposure could be tailored to not clip highlights).

And, yes, image averaging improves SNR by sqrt n, where n is the # of images averaged. This gets you pretty near the SNR of a n times longer exposure, except in some extreme cases, where the aggregate read noise from having read out n times as many pixels when you stack n images means the result is not exactly the same. But this is mostly academic.

And it's more that the signal's been amplified above the high (downstream) read noise floor w/ Canon at higher ISOs than that there's 'less electronic noise at higher ISO', though, yeah, the end perceived result is similar.

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Apr 28, 2015permalink

badi

Bwana, yes have a point is true and all that.

But the cited phrase is correct: you can't improve the signal-to-noise of a image no matter what. Yes there are techniques to get better SNR but that's another topic :)

@ Richard, Rishi - and actually it's such an interesting topic that i hope it finds a good place in this multi-part article.

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Apr 28, 2015permalink

SimenO1

Trying to improve shot noise by having longer exposures get ourselvs into a battle between dark current noise and read noise. This is very relevant when taking night scapes and astrophotos. Averaging many short exposures gives a lot of read noise, while having one extremly long exposure gives much dark current noise.

This was analyzed over at Clarcvision.com some years back with variable settings: http://www.clarkvision.com/articles/night.and.low.light.photography/

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Apr 28, 2015permalink

108

so for an amateur like me , what does that mean practically ? Are you saying you're shooting 4 times the same frame, same exposure parameters, and then you blend the lot and presto you have an image with half the noise a single shot would have produced ?

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Apr 28, 2015permalink

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bakhtyar kurdi

From experience I found something interesting, but I didn't know the reason, as we know stopping down the aperture gives sharper images until the diffraction starts,and we have a sweet spot depending on the pixel density of the sensor,usually around f8, there is something similar to that related to exposure time (shutter speed).

with longer shutter speeds, you get more saturated, less noisy images, but something similar to the diffraction happens in longer shutter speeds, the sweet spot is between 4-15 seconds, after that suddenly it gets worse and worse.

To make it simpler, if we take two images of the same sense, the first image taken at ISO 100, F8, 1/125 sec, then we take the second picture using ND filters until our settings become ISO 100, F8, 8seconds, the second image is more saturated, has less noise, better DR and much richer files.

I think this article explains my findings, what do you think?

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Apr 28, 2015permalink

Great Bustard

I think the exact same amount of light falls on the sensor in both cases as the longer exposure is simply a result of the ND filter lowering the light from the scene passing through the lens in the same proportion. That is, if your exposure time changes from 1/125 to 8 seconds at f/8, then you were using a 10 stop ND filter.

If the ND filter looks cleaner, it's due to the blur associated with motion in the scene.

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Apr 28, 2015permalink

bakhtyar kurdi

No, it is real, and a few people wrote about it, I didn't want to go to details, supposed most people know when we talk about 8 seconds we have first to stabilize our camera and taking picture of a still subject,so there is nothing to do with motion blur, yes we get exact the same amount of light, but less random photons.

Try by yourself those shutter speeds (3-15 seconds) , and you'll find even a P&S camera can produce amazing pictures.

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Apr 28, 2015permalink

Great Bustard

I invite you to start a thread on it in the PST Forum (Photographic Science and Technology Forum). Please post some examples if you have them. I'll look out for the thread, 'cause, I'm telling you, there is not less noise for an 8 second exposure at f/8 with a 10 stop ND filter than there is for an exposure at f/8 1/125 without the filter. If anything, there is more noise with the longer exposure due to greater thermal noise of the sensor with such a long exposure time.

Anyway, please, start the thread. Like I said, I'll look out for it.

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Apr 28, 2015permalink

Rishi Sanyal

Rishi Sanyal

No, Great Bustard is right - it's not the exposure length, it's the total amount of light. If you decrease the aperture n stops (or add a n stop ND filter), and increase the exposure time n stops, you get the same end result.

Except perhaps the longer exposure is worse if the exposure time is really, really long and you have thermal noise build up (dark current, dark current shot noise, etc.)

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Apr 28, 2015*permalink

SimenO1

There might also be the effect of mirror shake and shutter shake making longer exposures sharper. These shake sources affect the image most between 1/10 to 1/100 s.

At medium long exposures 1/10 - 10 s wind might effect a lot. At longer then 10s dark current and softness on the ground under the tripod might affect sharpness. A warm camera and lens in a cold environment might also give thermal focus creep at very long exposures.

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Apr 28, 2015permalink

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klausious

so I have a question: if i use the same lens 50mm at 1.8 on two different cameras: one is full frame and one is APS-C, beside the fact that the full frame will have a wider angle of view, will the image of the full frame be any better than the APS-C because keeping the same lens and same aperture will keep the aperture diameter the same and so to my understand that the lens will allow the same amount of light pass through the aperture, only that the full frame capture more of the scene and the APS-C doesn't.

The comparison in this article really doesn't help me because two camera and two different lens was used, and it was confusing for me. Right now i don't care about the angle of view. I just want to know if with the same lens and same lens setting, putting on two different camera system, which one perform better?

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Apr 28, 2015permalink

VidJa

The amount of light on the sensor per unit surface will be the same if you take a picture with lets say a 50mm @ f/2.8 and 1/250 s on a full frame sensor or a aps-c sensor.

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Apr 28, 2015*permalink

(unknown member)

The full frame sensor will have a larger area, so you either get more pixels of the same size, or larger pixels.

Larger pixels have less noise because they record more light and shot noise is = square root of signal.

However smaller pixels means more resolution. If you downsize the image to the same size, then you are combining the signals from the smaller pixels, so the result is the same. The larger sensor has less noise.

In other words, bigger sensor = more light = less noise.

It doesn't matter what lens you use if you use the same exposure for the same scene. It's the total number of photons that you record that matters.

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Apr 29, 2015permalink

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taojones

taojones

A good article Richard. Here is another good article written for canon cameras but applicable to other cameras regarding noise and ETTR

https://luminous-landscape.com/the-optimum-digital-exposure/

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Apr 28, 2015permalink

Lensmate

Lensmate

My thoughts exactly......this article came to mind as well....

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Apr 28, 2015permalink

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Skipper494

All very fine, but in film days we got grain from particles in the film, nothing from die film. As an engineer with quite a lot of experience in sensor design, I can assure you that most noise comes from the proximity of photo sites, or wiring, (even poor software) which is why lower resolution large sensors have less noise and more dynamic range.

Compare the Nikon D700 and the Sony NEX 7, for instance. Consider how good the Fuji S2 Pro was in it's day. Compare a lower resolution 1/1.7 sensor with a higher resolution 1/2.33, such as the Nikon P7000 with the Pan FZ35.

Frankly, too much emphasis is put on high numbers and marketing, instead of good photography results.

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Apr 28, 2015permalink

JackM

JackM

Lower noise, yes, more DR no. Compare D750, D810, and Sony A7S on dxomark.

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Apr 28, 2015permalink

Great Bustard

@Skipper494

Re: "As an engineer with quite a lot of experience in sensor design, I can assure you that most noise comes from the proximity of photo sites, or wiring, (even poor software) which is why lower resolution large sensors have less noise and more dynamic range."

I assume you mean most electronic noise, 'cause most of the noise comes from the light itself, with the exception of the portions of the photo made from very little light.

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Apr 28, 2015permalink

(unknown member)

@Skipper494

So how come the D7200 has more dynamic range than the A7mk2 (let alone the 5Dmk3).

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Apr 28, 2015permalink

Great Bustard

@57even:

Lower electronic noise at base ISO. However, DR is basically a measure of the shadow noise, the portions of the photo that receive less light. So, a camera with 14 stops of DR will have much cleaner deep dark shadows than a camera with 12 stops of DR, but this advantage will lessen, vanish, and reverse to favor the camera that gathers more light as you move away from the shadows.

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Apr 28, 2015permalink

Rishi Sanyal

Rishi Sanyal

It's actually more complicated. Most noise for most tones of most photographs comes from shot noise. Extra noise in shadows of low ISO files from Canon cameras comes from noise introduced in the signal pathway between the sensor/amplification, and the digitization of that amplified signal by an off-imaging-sensor ADC. The extra noise in shadows of the a7S compared to the a7R comes from - I think - extra quantization error from the huge FWC of the large pixels of the a7S paired with the limited bit-depth of the 14-bit ADC. But that's kind of an unproven pet theory of mine... it's fun though, b/c it goes against the grain of 'bigger pixels = less noise'.

Anyway, the discussion can get complex, and we'll try and break it all down in the next parts.

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Apr 28, 2015permalink

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cpt kent

Seems to be a lot of folks exclaiming brilliance without questioning. Sources? References? Research? Further reading?

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Apr 28, 2015permalink

Great Bustard

I know of at least one other source that would back it up. ;-)

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Apr 28, 2015permalink

Skipper494

There are a lot of sources touting the good of flu vacine, but the facts are that the UK government and others are suing the drug companies over useless vacine. There are always sources on both sides of an argument, each with their own agenda.

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Apr 28, 2015permalink

Richard Butler

Richard Butler

This was purely intended as a beginner's guide to... so there are no sources, per se beyond some conversations Rishi and I have had.

In terms of further reading, though, I believe Emil Martinec's much more thorough exploration is the place to go.

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Apr 28, 2015permalink

SmilerGrogan

Don't blame Mr. Butler for the gaping hole in this article. This is a persistent editorial blind spot at DPR. The editors should be insisting that the writers cite the authority for their claims and there should be interviews with respected authorities in the field. Instead, we are supposed to take it on faith that the writers know what they're talking about...Sure, it might be true, but it could also be a misreading of the relevant engineering texts, or the writer could have picked up information that's out of date, but we, the readers, can't judge because we're not given sufficient information about the sources used.

It's sad really, because this is otherwise a great and useful site.

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Apr 28, 2015permalink

Great Bustard

@SmilerGrogan:

I'm guessing you didn't click on Richard Butler's link and/or have no idea who the author of that link is. Might want to get on that.

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Apr 28, 2015permalink

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FuhTeng

FuhTeng

Excellent. Aside from trolls fussing about the validity of a metaphor, even the comments are helpful. I enjoyed it, thank you.

It seems like I'm always shooting with something clipped to white. I need to get better at fighting it versus going with it.

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Apr 28, 2015permalink

1971_M5

1971_M5

I have not read the post (yet) but the premise makes intuitive sense. Sometimes I shoot a scene and when I look at it afterwards, I'm thinking ... "Why all the noise?" and at other times I take a look and say to myself... "Wow... that's clean!"

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Apr 28, 2015permalink

Thuravi Kumaaran

Interesting article.

Expect more articles like this.

Wish to happen good things.

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Apr 28, 2015permalink

EvilTed

Underexposure and High ISO leads to more noise.

Awesome.

Thanks for enlightening us :)

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Apr 28, 2015permalink

J A C S

J A C S

It is not what the article says. High ISO does not lead to more noise per se.

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Apr 28, 2015permalink

panos_m

High ISO by itself doesn't lead to more noise. Underexposure does. The use of high ISO means that you uderexposing the sensor. Do you understand the difference?

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Apr 28, 2015permalink

Zapirian

Zapirian

Quite interesting that high ISO isn't what contributes the majority of noise to a shot, but it is what is often used to compensate when you can't help but underexpose the sensor.

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Apr 28, 2015permalink

EvilTed

Yes, I understand fine.

It's a triangle.

You get nothing for free :)

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Apr 29, 2015permalink

panos_m

What triangle? ISO is not part of exposure. Exposure is aperture and shutter speed only. ISO is a post processing step.

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Apr 29, 2015permalink

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Zumzifero

Nice article: so far i had never been aware of how much these camera resemble a professional phonometer. The signal to noise ratio and the amplification problems are almost the same, including adapying the output signal to known function which resemble the human eye.

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Apr 28, 2015permalink

Earth Art

Thermal conditions make a huge difference in shot noise as well. Big difference shooting at night in 30 deg F and 80 deg F.

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Apr 28, 2015permalink

dosdan

That's not shot noise. Rather it's dark current & thermal blooming if parts of the sensor (the columnar ADCs situated on the edge) are operated in a long enough exposure.

Shot Noise aka Photonic Noise is related solely to the number of photons in the capture. It's an intrinsic property of light, so it can't be avoided.

Dan.

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Apr 28, 2015permalink

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Mikity

Good article. I think the changing exposure/changing ISO section is needlessly convoluted though - and it's not obvious you can hover over the images!

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Apr 28, 2015permalink

Richard Butler

Richard Butler

I take your point, I'm just not sure what I can do to make the 'buttons' more obvious, without breaking our style sheet.

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Apr 28, 2015permalink

tlinn

tlinn

Totally missed the hover feature. Those illustrations make much more sense now. Richard, perhaps just a caption reminding users that they can hover?

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Apr 28, 2015permalink

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Anastasiadis Lazaros Thessaloniki Wedding

I read the article and I personally don't agree with a lot of things. Raindrops inside tubes don't behave like light in photos, sensor size does not matter the technology and quality of the sensor does not have to do with its size. This article tries too hard to impress the amateur photographer with magic tricks but actually it does not offer anything new except maybe some confusion about how you should take photos without much noise.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

The technology and quality of the sensor certainly have a role to play, but that's what part 2 of the article will be about.

However, with the exception of some quite specific examples, the dominant source of noise in most tones in most photos comes from shot noise: not the camera. And the sensor size generally plays more of a role than the specifics of its technology.

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Apr 27, 2015permalink

Iliah Borg

The original object to study this type of noise were shot towers (used to manufacture lead shot), so, yes, rain parabole works ;)

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Apr 28, 2015permalink

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Jonathan Lee

Kudos, Richard. i appreciate the clarity you've gone in length on this topic with vivid illustration.

were u a professor in past life? :)

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Apr 27, 2015*permalink

tlinn

tlinn

Great article, Richard. A couple questions:

1) Does shot noise present as primarily luminance noise or color noise too?

2) Am I correct to infer that part 2 of this series will answer the question of whether or not it is beneficial to ETTR at ISOs other than the base ISO?

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Apr 27, 2015permalink

Richard Butler

Richard Butler

1) My understanding is that it appears as both chroma and luminance noise, but there may well be people able to give a more precise answer than this.

2) Part 2 will address why the best approach varies between cameras and will clarify the sections of our reviews that look at this.

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Apr 27, 2015permalink

Sessility

I think the difference between chroma noise and luminance noise is a very important distinction. This is where there's still a great deal of difference between cameras - the algorithms and more importantly differences in the sensor's color filter arrays, and I think the majority of people find chroma noise much more irritating than luminance noise (which looks more like traditional grain).

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Apr 28, 2015*permalink

(unknown member)

Richard Butler- hope the 2nd part takes into account the DR window shift.. like the Old Olympus e-620 to current. :-)

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Apr 28, 2015permalink

SimenO1

All photons have a single distinct color or wavelength. So physically luminance noise doesn't exist. Its all chroma noise. But color filter arrays doesn't filter exact wavelengths. The filters are covering a wavelength spectrum even with overlapping to other colors. Its the with of the color spectrums and amount of overlapping that makes a balance between chroma and luminance noise in a raw image, and software that further adjusts the balance.

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Apr 28, 2015permalink

(unknown member)

Actually you can indeed talk about Luminance noise. The photons themselves don't have it, that's the sensor. The sensors without a color filter array all they can see is Luminance. The noise coming from electrical/electronic issues on the sensor, not the photons.

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Apr 29, 2015permalink

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falconeyes

falconeyes

Interesting and important article.

However, it should have used fewer words. The article makes a simple matter look more complicated than it really is. And may discourage some to read it.

Everybody thinking that noise is (mostly) a camera artefact should read the article tough.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

Thank you. And I must admit it's ended up longer than I planned.

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Apr 27, 2015permalink

falconeyes

falconeyes

Thanks for replying.

BTW. one of the most interesting topics left in camera technology (and rarely discussed) is the suggested ergonomics of an isoless camera. An isoless camera (covered in your Part 2, I guess) has no read noise/dark current/quantization noise and therefore, no native iso setting. And no simulated one too as it would cripple the highlight capacity (FWC) for no good reason.

But a photographer would STILL want to tell his camera to use more or less light, depending on the shooting situation. And he would STILL want to tell his camera of he wanted the images darker or brighter in appearance. All w/o an ISO setting. This will become an interesting conversation in the future.

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Apr 27, 2015*permalink

b craw

b craw

Length is reasonable; a well-presented primer on the subject. As evidenced by the minutiae in the comments, some length is required.

Excellent use of analogy, btw. A fair number of photographers will go to bed tonight with a few more packets of understanding in their test tubes. [Unfortunately, some won't be happy until they can deploy any information in a gear turf war.]

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Apr 27, 2015permalink

Richard Butler

Richard Butler

It's something I've been thinking about recently (and whether we should expect this from a camera company or from independent developers). The Auto ETTR stuff that Magic Lantern are doing support my theory it'll probably be the latter.

As soon as you start thinking through the implications of a true ISO-less camera, you realise how much of conventional camera design you would probably end up throwing away (which I think makes it more likely that these changes would come from outside the industry).

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

I think the best implementation of 'ISO-less' would be fairly transparent to the photographer; the photographer would use the camera pretty much in the same manner they currently use it, they'd just suddenly realize there's a ton of highlight information they can recover in high ISO files that with traditional cameras would be blown.

That way they don't have to completely overhaul their way of thinking, though there's also something to be said for a camera that can 'Auto ETTR' - with some options as to limits on midtone SNR, or % of contiguous pixels that can be clipped, etc. Or what the camera should consider a point source & allow to clip.

Currently, though, there's still some quantization error when 'hacking' cameras and using them in an 'ISO-less' manner (by severely underexposing by dialing down your ISO while holding focal plane exposure constant). We need higher bit-depth ADCs given current FWCs (or, smaller & more pixels to lower FWCs to the max DN of lower bit-depth ADCs).

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Apr 28, 2015permalink

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ImagesToo

Quite well explained except for one major mistake. You talk about sensor size as being important. It is only part of the story. The real issue is pixel size. A FF sensor with 4 times as many pixels as a 4/3 sensor is identical in noise performance as each pixel is now only 1/4 the area so it captures the same amount of light.

The other thing which has been omitted is that because of shot noise a raw file only contains about 250 levels of brightness for a pixel which is what a jpg file has. Virtually all the extra information in a raw file is nothing more than digitised noise. You can do the calculations quite easily remembering that noise is the square root of the number of photons.

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Apr 27, 2015permalink

Andrew53

Shot noise is the amount of light per unit area. This applies to an individual pixel and an entire picture. For the same exposure (i.e. the same intensity and same time) the noise will be the same for a given area. While a single pixel may have more noise (because it is smaller) the overall signal-to-noise will depend on the area. So larger sensors produce lower noise because they collect more light - for the same exposure.

But...

For an equivalent DOF and equivalent focal length and the same shutter speed there is (in theory) no advantage to a larger sensor.

A m43 25mm using ISO 1600 produces the same (shot) noise as a FF 50mm f2.0 at ISO6400 using the same shutter speed. (in theory) and at the same time should produce the same field of view and the same DOF.

There is no free lunch however, because building f1.0 lenses is difficult, heavier and more expensive. Zoom lenses even more difficult and heavy - and expensive.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

Thank you @Andrew53, that's exactly right. One thing perhaps worth mentioning is that that 25mm f/1.0 shot will blow pixels more easily than the FF, b/c there's 4x as much light per unit area on the sensor, and full-well capacities of pixels are not infinite. Which is another reason behind the 'no free lunch' concept.

Essentially, with a smaller sensor, you can compensate for the smaller surface area by sending more light per unit area to the sensor, but that only works up to a certain point, since pixels do saturate.

Oddly enough, though, for the FF to give you this advantage of 'not blowing as quickly' from the lower light per unit area, you also have to keep your ISO down (say, at ISO 1600 in your thought experiment above), since hiking up the ISO decreases effective full-well capacities of pixels.

Which is why we've been introducing and harping on the concept of 'ISO-invariance'... i.e. saving that brightening for later, rather than raising the ISO to 6400.

More to come... :)

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Apr 28, 2015permalink

Jacques Cornell

Jacques Cornell

I used to believe the ideas in the first paragraph, but the consensus of experts now seems to be that sensor size, not pixel pitch, most affects the noise level.

As for the second paragraph, a JPEG has 8 bits of luminance data per pixel. This represents 256 levels of brightness. OTOH, most RAW files contain either 12 or 14 bits of data, which equals 4096 or 16384 levels. Whether this full potential is actually reached, I don't know. But, I think pretty much everyone agrees that RAW files provide highlight recovery and can withstand shadow lifting and tonal stretching far better than JPEGs because there are more levels available.

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Apr 28, 2015permalink

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nunatak

thanks ... an informative article. i'm looking forward to the rest of this series.

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Apr 27, 2015permalink

AksCT

Nice article and simple description of effect of shot (quantum) noise. To be precise, quantum noise is statistically square root of signal, i.e. for every 100 photons, you will have (statistical mean) of 10 quantum photons/noise. So the ratio of noise to signal photon would be 10/100=10% (this is not SNR or inverse of it). Here is an example:

10 photons ->sqrt(10)~ 3.3 => ratio 3.3/10=33% (very dark region)

100 photon -> sqrt(100)=10 => ration 10/100= 10% (dark grey)

100000 photons -> sqrt(10000)=100 => ration 100/100000 = 1% (bright region)

As you can see, within the same image (as shown by your pictures) ratio of noise to signal can vary from 1% (barely visible) to 33% (very noisy).

Quantum noise is inherent nature of CMOS/CCD detectors.

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Apr 27, 2015permalink

ImagesToo

Quantum noise is inherent in light and has nothing to do with how you detect it.

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Apr 27, 2015permalink

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rgames1

Interesting but I'm skeptical that the variation in number of photons can cause anywhere near the amount of noise produced by the camera electronics.

The argument is made by comparing to tubes collecting raindrops. However, nowhere in the article does it say how many photons are captured in the shadow pixels, so the comparison is never backed up with any data. Making the argument requires that that number be established then compared to the variation in number of photons.

So, how many photons are captured by each pixel in the shadows? Further, what is the variation in that number? My strong suspicion is that the variation in number of photons in any part of the image is still extremely small compared to the number captured but that information is nowhere to be found. That information is implied by the analogy but never quantified.

The answer to those questions will show whether or not the analogy is valid.

rgames

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Apr 27, 2015permalink

rgibbons

rgibbons

rgames1 wrote: " That information is implied by the analogy but never quantified."

When I take astronomy pictures of dim nebula, the darker points have tens of photons per pixel. The nebula I want to see have hundreds of photons per pixel, and the brightest stars have tens of thousands of photons per pixel. Pixels themselves max out after holding several tens of thousands of pixels (well-capacity). I need to take exposures for hours, with a large aperature telescope to expose the dimmer nebula (stacking pictures taken over several nights).

In the cool winter, the sensor noise is negligible. On a warm summer evening the sensor noise becomes very noticeable (increases exponentially with temperature), and I need to take "dark" exposures to subtract the sensor noise from the real signal in the "light" exposure.

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Apr 27, 2015*permalink

(unknown member)

In other words, the ratio of photons captured in the brightest part of the image to those captured in the dimmest part of the image can be 100:1 or greater.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

As mentioned in the article, shot noise is equal to the square root of the signal, which means that a signal of, say, 9 has a deviation of ±3. Since upstream, sensor-level read noise of cameras (which we really didn't want to get into in part 1) has been brought down to really, really small numbers (e.g. 1-2 or 3 electrons), that means that shot noise is still a large component of the noise, usually the larger component. For a signal of 100, the shot noise ±10, for example.

There are cases where the electronic noise supersedes the shot noise, of course, such as when downstream read noise*, which can reach as high as ~30 or so electrons, according to sensorgen's extrapolations of DXO data. In that case, it can start encroaching on or exceeding shot noise, and you'll see that in shadows/midtones, especially when pushed.

*Noise introduced after sensor readout and ISO amplification, which can be pretty high in architectures that don't have on-chip ADCs.

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Apr 27, 2015*permalink

ImagesToo

The article is correct. A typical pixel captures a maximum of around 64000 photons. The first stop has 32000 photons, the next stop has 16000 photons. By the time you get 6 stops down you are around 1000 photons with noise of +-30 photons. 8 stops down you have 250 photons with noise of +-16 photons, 10 stops down and you have about 65 photons with a noise of +-8 photons which is going to make a very blotchy image.

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Apr 27, 2015permalink

Dpreviewmember

Dpreviewmember

Sorry Rishi but I have to agree with rgames1 in this case, at least with small sensor cameras like mine the thermal and/or circuit noise is way more evident than the random nature of gathered light.

This electronic noise is larger the longer the exposure so in practical terms each sensor-camera-lens combination probably have an optimal exposure time versus available light.

A simple sensor test (see my gallery) can prove that :

just put the cover in your lens, let the camera inside the bag in a completely dark room and take pictures at different ISO and shutter times. Since there is no light at all the illuminated pixels are pure electronic noise.

My small sensor cameras look like a starry night.

Noise is random contrary to signal, so if the camera took a burst of pictures of in succession and added them the signal to noise ratio would be larger, similar to old CD disk players from the 90s when their advertising would say things like "16 times oversampling".

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Apr 27, 2015*permalink

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russimages

An Interesting piece, which I think I understand at a conceptual level. But I'm not sure of the pragmatics of it. Most of my shooting, whether of birds & wildlife or the occasional landscape or sports action, is opportunistic, i.e., I'm not there with a planned image, I usually don't have time to check the histogram and adjust to the right, and my priority is usually freezing action and avoiding shake, which means higher shutter speeds. My approach is to understand for any given body the ISO at which shadow noise becomes a problem. I then shoot in manual mode with spot metering and with auto ISO, with the highest end of the ISO range set below the problematic level for correctable shadow noise. I shoot what I get and post process to recover shadows, among other things. With this approach I don't encounter noise that is a problem, and I seldom blow highlights. Based on the present DP article, what should I be doing differently?

https://www.flickr.com/photos/russ-w/

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Apr 27, 2015permalink

Bernard Carns

@russimages "I usually don't have time to check the histogram and adjust to the right" Some camera manufacturers do this for you like with the Black Magic Pocket cinema camera. People like Michael Reichmann (Luminous Landscape) have asked for his ability in SLRs for years.

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Apr 27, 2015permalink

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jl_smith

This is awesome - I can't wait to apply this knowledge to take better photos of cats, or at least things sitting on my desk

:D /jest

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Apr 27, 2015permalink

(unknown member)

One of the take-home messages is to ensure all your cats are mid-grey or lighter.

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Apr 27, 2015permalink

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Dantist

Sorry guys, but term "shot noise" is a complete and utter nonsense in context of normal photography. Just try to calculate photon flux (# of photons) for typical light conditions. Yes, everything boils down to available signal to noise ratio, and part on ETTR etc is absolutely fine, but the main noise source is sensor itself and read-out electronic, and thats why Sony A7s can shot at ISO100000, whereas Canon 1Ds is limited to ISO 1000 (~same sensor size and pixel count). Moreover, cool the later with liquid nitrogen, and the ISO 100000 could become possible as well :) That's why astronomical detectors are only operated cooled to -70C or so. And even then, in most cases electronic noise dominates photon shot noise (and yes, I'm a professional astrophysicist).

Just to give a number:

Flux from a overcast night moonless sky is ~1e-4 lx = 1e-4*(0.019*6e23 to convert to photon flux)*(7.2e-4 multiply by area of 15.2mm aperture)/(16e6 divide by pixel count)~5e7 photons per pixel per second.

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Apr 27, 2015*permalink

HighLowISO

I wish the authors would respond to your comment. I have no idea what you're talking about, but my gut tells me that at the light levels we are working with for photography you are absolutely right. Maybe we'll get a few more astrophysics commenting or even some professional astronomers, as a gut feeling is not always right.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

No, 'shot noise' is not 'complete and utter nonsense in context of normal photography.'

In fact, I'm curious as to what you define as 'normal photography', considering you cite examples of (1) ISO 1 million, & (2) astrophotography - neither of which are 'normal photography'.

You can cool your sensor down all you want, but that's not going to make ISO 1 million suddenly look great on any camera. That's because full-well capacity at ISO 1 million is already so so very low that your image has to be made up of very few photons. For example, at ISO 409,600, 'white' (blown pixel) is generated from something like ~50 photons. That means your brightest tone still only has a best possible SNR of sqrt(50)=7. That means a midtone 3 stops from clipping (w/ a signal of 6.25) has a SNR of 2.5 even w/ 0 read noise, which is even below the SNR cutoff some use for dynamic range calculations.

Yes thermal noise & read noise will make that even worse, but shot noise has already heavily limited you.

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Apr 28, 2015permalink

Dantist

Actually, you can still refer to electronic noise as "shot noise", but that's imho misleading terminology as you're not dealing with poisson process here. Basically, you get "shot-noise" like behavior when the charge induced by incident photon flux gets comparable to intrinsic detector noise level. In this case you can not discriminate the two and get random fluctuations similar to the shot noise (although its statistical properties are different). However, this limiting level is defined by detector noise and not by photon flux fluctuations in consumer photography. That was my point. You can check my words yourself by pushing a low-brightness high iso raw file to extreme. The "banding" immediately becomes apparent with any modern sensor, and this noise is only associated with the sensor itself and has nothing to do with what you photograph. You can get rid of it by developing better sensor or cooling it down, so the future remains bright :)

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Apr 28, 2015permalink

SwissRapha

@Dantist:

I am not an astrophysicist, but I think you forgot a factor of 1e-6 in your calculation. The conversion factor from lux to photon flux is 0.019 MICROmols, isn't it? So you should only multiply by 6e17 instead of 6e23. Please correct me if I am wrong.

So, if we assume a 'normal' scene:

overcast day, close to dawn: scene illumination 100lux

normal gray reflection factor: 0.2

50mm, f/4

we need to freeze some motion, so 1/200 shutter time

16MP

photons per pixel = 100*0.019*6e17*(0.0125^2*pi)/16e6/200*0.2 = 35e4

Ok, that's still a lot of photons. But if you now have some dark parts in the scene with a reflection of less than 1%, you'll start to get into areas where shot noise is visible. Now move the scene indoors into a dimly lit bar where you try to take a picture of a singer, you will certainly be photon starved...

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Apr 28, 2015*permalink

SnakePlissken

All this discussion does is reinforce how utterly boring hardcore techie digital photographers are. Tons of great images taken before the advent of digital photography had loads of noise, it was a fact of life about ISO200. Never ceases to amaze me how tedious the threads are on here with know-it-all techie bores.

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Apr 28, 2015permalink

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RichRMA

FF cameras will likely always have better noise control than smaller format bodies, but as they creep up in pixel count we've seen an increase in image noise. The D810 is visibly noisier than the D4s, for example, solely due to pixel size. There will come a point where (if they get to 80-100mp) a FF will be noisier than a standard 24mp APS. Couple that with sensor differences (example, Samsung's backlit or Fuji's sensors) and different in-camera processing and the idea of absolute noise control based solely on sensor size becomes less "absolute."

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Apr 27, 2015permalink

HowaboutRAW

And better lenses will help in either case--FF or APSC.

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Apr 27, 2015permalink

(unknown member)

What happens to all that noise when you downsample your 100MP image to 24MP?

If you compare a 100MP FF and 100MP APSC, how does the FF sensor do in that scenario?

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Apr 27, 2015*permalink

RichRMA

I'm still not convinced a downsampled D810 image is as good as a non-downsampled D4s (or D3s for that matter) image. There is a pixel-size barrier where not enough photons can "fit" in the pixel well to be overcome by comparative downsampling.

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Apr 27, 2015*permalink

Rishi Sanyal

Rishi Sanyal

The n times higher resolution sensor does have n times more pixels to read, and therefore more aggregate read noise; however, you have to balance this by accounting for normalization, since we tend to look at images, not pixels.

Once you account for normalization, if an n times higher resolution sensor can scale down its pixel-level read noise by sqrt(n), it'll actually have the same exact normalized noise as the n times lower resolution sensor.

A good example of a higher res camera that reduced per-pixel read noise enough to compete with, even outcompete, its lower res brother is the D7100 vs the D7000, here.

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Apr 27, 2015*permalink

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Felix E Klee

Felix E Klee

For the second article: When discussing the DP1x in the forums, I've been told that certain Sigma cameras always record the Foveon sensor's information at base ISO, i.e. with fixed amplification. It isn't necessary to adjust ISO in camera. One can just look at the histogram, expose to the right, and later in Sigma Photo Pro adjust the tone curve to one's liking. In other words: At identical shutter speed and aperture, an image shot at ISO 100 and adjusted EV+1 in software is identical to an image shot with the camera set to ISO 200.

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Apr 27, 2015permalink

Mescalamba

Yep, they are "software amplified".

Also reason for horrible noise on anything else than ISO 100 (well its pretty noisy even on that).

Sigma desperately needs tech update.. even more than Canon. xD

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

So the thing is, you shouldn't amplify in software if your camera is not ISO-less (for example, pushed base ISO files from Canon cameras don't look as good as those amplified via hardware, ISO amplification, b/c of their high downstream read noise). We wonder if Sigma cameras are not actually 'ISO-less' or 'ISO-invariant' at the hardware level, which is why their 'high ISO' files fall apart - b/c they're essentially amplifying a source of read noise that wouldn't have been amplified had the signal been amplified prior to the addition of that source of noise.

... it gets a little complicated, as you can see, which is why we'll try and break all this down in the next part.

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Apr 28, 2015permalink

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Reivilos

Reivilos

Thanks for this article.

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Apr 27, 2015permalink

Rex1227

Does that mean the a shot at a specific ISO cannot get any cleaner up to a point since the amount of photon noise cannot be reduced?

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Apr 27, 2015permalink

Richard Butler

Richard Butler

Yes.

For each sensor size, f-number and shutter speed, there will be a certain amount of shot noise associated with each tone in the image. That will act as a hard limit on how good a particular ISO setting can get.

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Apr 27, 2015permalink

Mescalamba

No regular camera came to that point so far..

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Apr 27, 2015permalink

deep7

Eric Calabros: The trouble with using a faster lens/bigger aperture is that you lose depth of field. That's limits the advantages of a larger sensor, in a practical sense, if you want to control your depth of field (rather than just having it as shallow as your lens allows).

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Apr 27, 2015permalink

thx1138

thx1138

Yes if you had ideal electronics and there were no other sources of noise, the shot noise would be the noise floor.

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Apr 28, 2015permalink

Rishi Sanyal

Rishi Sanyal

Eric: the other problem with just using faster and faster lenses, or simply giving the camera more and more exposure (longer shutter speeds) is that you run into pixel well-capacity limits. Which has implications for dynamic range. The only way to overcome this currently is to grow the surface area of your sensor, which is why larger sensors - all else equal - have more dynamic range than smaller sensors.

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Apr 28, 2015permalink

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HowaboutRAW

"it [noise] comes from the light you're capturing."

Meaning optically better lenses help with noise.

Oh wait, that's been clear for years, despite vociferous denials in these comments.

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Apr 27, 2015permalink

Mescalamba

They also help with color separation (read - Zeiss/Leica/Voigtlaender .. and suprisingly Samyang). Some L glass too.

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Apr 27, 2015permalink

HowaboutRAW

Yep.

Yep Samyang. Some Samsungs too.

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Apr 27, 2015permalink

ImagesToo

The is not right HR. The quality of the lens has nothing to do with shot noise. Shot noise is a property of light. A better lens will help with sharpness, chromatic aberrations and things like that it does absolutely nothing to noise.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

No, HowaboutRAW. Unless by 'better lens' you mean a lens that lets in more light.

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Apr 28, 2015permalink

SwissRapha

Well, it would be great if all lens producers also publish T-stop information along with F-stop, not just for video oriented lenses.

Rishi, given your joice of using the ZA 50mm instead of the Sigma art in the Sony A77II test, HowaboutRAW is somewhat right if one considers a lens with better light transmission being a 'better lens' overall. Which of course is too simplified...

BTW, Rishi and all other dpreview staff, thanks very much for your articles and your participation in the comments/forum. Don't let the impolite members discourage you!

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Apr 28, 2015permalink

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Conjure

Conjure

PLATIN AWARD for this article!

Looking forward for part 2

Thank you

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Apr 27, 2015permalink

TPS88

Thank you for a very clearly written article. I can't wait for part 2.

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Apr 27, 2015permalink

snapster

The section on the effect of sensor size on noise only applies if the sensors have the same number of test tubes (pixels). With the same number of pixels, each individual pixel on the larger sensor receives more light. If the pixels are more or less the same size i.e. pixel pitch is similar then both sensors should have the same noise although the larger sensor will have a higher resolution (more pixels)

Using the example of two same size sensors, one having 24Mp and the other 12Mp, the 12Mp sensor should have less noise. Same as having two same size rectangles with one containing 100 test tubes and the second containing 50 test tubes of double diameter. The 50 test tubes would each have more water than the smaller test tubes although the total water captured by both rectangles would be about the same.

As for shooting to the right, this may depend on the sensor. The dp review of the Nikon D5500 observed that it has an ISO insensitive sensor. Check out section 9 in the review

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Apr 27, 2015*permalink

HFLM

Per pixel yes, but when the larger MP sensor image is downsized to the 12MP image, the difference shrinks.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

We'll talk about the case of more vs. less pixels on larger vs. smaller sensors in either part II or maybe even part III, b/c a proper discussion of all implications of pixel size requires an understanding of read noise, which is the subject of part II.

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Apr 28, 2015permalink

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RichRMA

"Output size" I thought was determined by pixel count?

"In turn, this is why we talk about different sensor sizes representing an image quality/size/price balance: because, so long as the sensor's electronic performance is similar, the effect of shot noise means that sensor size is the major determinant of image quality. Yes, pixel count can make some difference, but shot noise tends to play a much bigger role, if you compare images at the same output size."

If you cut a FF sensor in 4 parts, essentially making it a 4/3rds size sensor, the individual pixels will still render the same noise as when it was a full-frame sensor. Overall light collection does not effect the response since the pixel size does not change and therefore the noise will not change. You could do an experiment by inserting a physical cropping mechanism in front of the FF sensor and see this is the case. All that will happen is the angle of view of the scene will be cut in half, which has no impact on noise.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

Output size is entirely up to you. View images on your monitor or print them out and you've probably rescaled. It's certainly unlikely that you'd choose the size based on the captured image's native dimensions.

Take a 1/4 crop from a full frame image and yes, the pixel-level noise will be identical to any other part of the full image (and to a 4/3rds size sensor). However, scale (up or down) the image to the same viewing size as the whole sensor image and the noise will be more apparent.

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Apr 27, 2015permalink

RichRMA

Yes, that much is clear. Has anyone scaled-up a Nikon D4s image to the size of a D810 and seen if the noise matches?

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Apr 27, 2015permalink

Iliah Borg

Upsizing a demosaicked image is not a convincing procedure. You can try upsizing binned images.

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Apr 27, 2015permalink

RichRMA

Do any cameras do binned images in-camera these days? Or must it all be done in post-processing?

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Apr 27, 2015permalink

Iliah Borg

Yes, it needs to be done with raw data out of camera. But there are also other ways to compare noise, however those methods are not direct visual.

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Apr 27, 2015permalink

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Discovery Of Light

Discovery Of Light

Hey Richard! How does Lytro handle all these misbehaving photons? Do their cameras become radioactive like the RX? Sorry couldn't help myself.

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Apr 27, 2015permalink

morepix

morepix

AFAIK, autoexposure now works by modulating light acceptance to the brightness of average gray. Could that algorithm, in a future sensor design, be modified to implement ETTR?

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Apr 27, 2015permalink

(unknown member)

With apertures and shutter speeds we talk about in photography, I am almost sure photons come into the camera at a faster rate and in a greater number than rain drops into the test tubes, even figuratively spoken. There is no such thing as a non-uniform distribution due to that effect.

Nota bene: Rain collecting test tubes do not suffer from cross-contamination (not even due to a high gain factor).

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Apr 27, 2015*permalink

mpgxsvcd

This is the first time that I have seen shot noise factored into the argument that the larger the sensor the better the noise characteristics are. That is why I was finding it so difficult to accept this as fact before.

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Apr 27, 2015permalink

Felix E Klee

Felix E Klee

Actually that's not true. What matters is the combination of sensor size and aperture.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

Actually, yes it is true, since the combination of sensor size, and aperture, and shutter speed determine how much total light you capture for any scene element, which in turn affects the total shot noise contribution, which ultimately determines your SNR for that scene element.

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Apr 28, 2015permalink

mgrum

Indeed, upgrading to digital medium format gains you pretty much nothing in terms of total light gathering as there are almost no fast lenses available.

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Apr 28, 2015permalink

Felix E Klee

Felix E Klee

One should differentiate between relative aperture value (f-number) and the diameter of the aperture. At the same field of view, cameras of different sensor size will record the same amount of shot noise, if they are triggered with identical shutter speed, and if the diameter of their apertures is the same. Sensor size is irrelevant.

As explained in the article, the diameter of an aperture at f/5.6 on full frame is the same as that of an aperture at f/2.8 on MFT, of course only at identical FOV.

So I take back what I said earlier: What matters is not the combination of sensor size and aperture. It is the combination of shutter speed and aperture. That's what the article is about, after all.

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Apr 28, 2015*permalink

mpgxsvcd

@Felix E Klee

Actually that isn’t true. Your mistake is that you assumed that the smaller sensor uses all of the light that the aperture can provide. If the lens illuminates the entire full frame sensor then the smaller sensor will literally discard a portion of that light because the light falls outside of its area. That will also decrease your signal to noise ratio because you are discarding some of the light and the shot noise and absolute aperture haven’t changed.

I made the same mistake in one of my questions as well.

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Apr 28, 2015permalink

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firozansari

Very informative!! Thank you for publishing this article. We need more articles like this on DPReview.

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Apr 27, 2015permalink

LensBeginner

LensBeginner

Very clear explanation, much appreciated.

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Apr 27, 2015permalink

mpgxsvcd

A requirement for registering for this site should be that you have to read this article first.

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Apr 27, 2015permalink

JPinIE

If you use a graduated filter & hold back the brighter parts (usually sky), & expose correctly, does this mean that the darker parts receive more light & then less noise. I find using grad means longer shutter speed & brings the tones within what the camera can handle ev wise.

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Apr 27, 2015permalink

Androole

Pretty much. Though there's not usually a whole lot of reason to faff around with grad ND filters and their issues with uneven horizons when you can just do an 5-EV bracket and merge to HDR.

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Apr 27, 2015permalink

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jon404

***** Five-Star Article!

Thanks, Richard. Your writing is so clear and informative... VERY much appreciated.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

Credit should also go to Rishi. This article stems from many, many discussions about noise, sensors, the ISO standard and how people use cameras. It wouldn't be the same article without his input.

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Apr 27, 2015permalink

Luke Kaven

This article continues a trend favoring editorial quality in the last couple of years. I especially appreciate the fact that in this case you did not attempt to oversimplify a subtle scientific and technical issue, and in doing so, you've done a great service to your readers.

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Apr 28, 2015permalink

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Photato

Photato

About Sensor Size.

Strictly speaking Sensor Size should not be a factor in Noise, because lenses can concentrate the same light (photons) in a large or small area.

So much so that you can start a fire concentrating Photons with a magnifying glass in a small area.

What happens is that normally smaller sensors have a higher Density of pixels making it less efficient in photon collection.

For instance. A Small Sensor filled with 8 Micron Pixels should be able to collect the same amount of Photons than a Bigger Sensor filled with 8 Micron pixels. The difference is that the Bigger Sensor would have higher resolution.

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Apr 27, 2015*permalink

Richard Butler

Richard Butler

If you could make small pixels with the same full-well capacity, then yes, you could use something like a SpeedBooster to condense the light down onto a small sensor, and hence get the same light capture and the same noise performance.

Without this, if you have the same pixel size, then the pixels on the smaller sensor over-expose faster (because you've condensed the light into a smaller area, so each pixel on the smaller sensor now receives more light). You then have to reduce exposure to protect the highlights and you end up back at the same point: with the smaller sensor getting less total light and showing its shot noise more readily.

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Apr 27, 2015*permalink

mpgxsvcd

The speed booster would change the focal ratio though. Thus the images would no longer be equivalent.

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Apr 27, 2015*permalink

Photato

Photato

@Richard, Agree but I was not talking about matching resolutions with Smaller Pixels.

The Smaller Sensor with Same Pixel Size would have same Sensitivity as the Larger Sensor so no need to reduce exposure.

The only difference would be the Final Image RESOLUTION.

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Apr 27, 2015*permalink

Richard Butler

Richard Butler

mpgxsvcd: he was suggesting 'condensing' the light that would usually cover a large sensor down onto a smaller size.

Which, as you say, changes the net focal length and hence the f number.

Eg: 35mm F1.8 on FF vs the same lens with a 0.66 condensing lens behind it. The net focal length of the 35mm lens and condenser would be 23mm. On this shorter focal length, the (unchanged) aperture would now give an f-number of f/1.2.

Consequently, a 1.5x APS-C sensor would see the same field-of-view as the full frame sensor, but it would experience greater light per-unit-area if the lens was left wide-open. So you'd get the same field of view and the same depth-of-field but, since you're essentially now using a 23mm f/1.2, you'd be more prone to over-exposure if you kept the same shutter speed.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

Photato: there are always complicating factors (for instance a pixel that captures too much light means you can run out of bit-depth to fully encode everything it's capturing in the shadows), but broadly speaking, shot noise plays a larger role in most situations.

Part 2 will talk more about the role of electronic noise (though it'll need a much more length piece or, perhaps, a book to detail every possible source of noise covering every possible case).

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Apr 27, 2015permalink

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mpgxsvcd

Does the size of the sensor become less and less important as the shutter duration becomes longer? The shot noise should become more consistent with longer durations but the electrical noise should increase. If the sensors are made from equal technologies then the contribution of read noise should be consistent per unit area between both sensors.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

"Does the size of the sensor become less and less important as the shutter duration becomes longer?"

No, b/c the larger sensor still has a larger total full-well capacity * # of pixels, which means it can still collect more light overall. In other words, you can't just keep throwing more light at the smaller sensor - pixels have finite well capacities, so you can't always compensate by giving the smaller sensor more light ad infinitum.

Read noise gets a bit more complicated. Aggregate read noise depends on # of pixels & per-pixel read noise, and then any downstream read noise added between sensor readout & amplification and digitization. There are too many factors to talk about here to simply generalize and say 'read noise should be consistent per unit area'...

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Apr 28, 2015permalink

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stevevelvia50

If you want to take the exact same image, same DOF using the same shutter speed.

Full Frame: F 22, 1/500 sec (ISO set to 3200)

Dx: F 16 1/500 sec (ISO set to 1600)

Micro 4/3 F 11 1/500 sec (ISO set to 800)

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Apr 27, 2015permalink

mpgxsvcd

F11 is never good for any native Micro Four Thirds lens.

I wonder how aperture affects shot noise. Shot noise must be very high for extremely small apertures and then decrease parabolically as aperture is increased. At some point shot noise would become inconsequential even at very short exposure durations if your aperture were large enough. That number is probably huge though.

Typically astronomers simply say “Bigger is better in reference to the aperture of a telescope”. However, at some point increasing the aperture should have little shot noise gain especially if you factor in the cost increase for that larger aperture. Now it will always give you a resolution advantage no matter what.

The Hubble telescope has a 7.9 foot diameter while the upcoming James Webb Space telescope has a diameter of 21 feet. That makes even telescopic full frame lenses look like tooth picks.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

@stevevelvia50: Yes... that's essentially correct. A very limited case, but correct. I say 'limited case' b/c generally you're not that constrained... you can either use a longer shutter speed or faster aperture to let in more light and reduce noise. OTOH, you can also dial down the ISO setting and give yourself more highlight headroom (assuming you're relatively 'ISO-invariant' or 'ISO-less' at that point).

So there are still, generally speaking, a number of advantages to be had with the larger sensor.

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Apr 28, 2015permalink

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mpgxsvcd

If Dpreview gave awards for articles like they do in camera reviews this one would get a unanimous Gold star.

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Apr 27, 2015permalink

joe6pack

The way I do ETTR is I use multi-metering and set the exposure compensation to +1.0Ev or up to +1.7Ev when I am outdoor. I can say that I have at least overcome the ISO 200 limitation on my NEX-3N. However, a couple of downsides are:

More edits needed. Almost all RAW files needs reduced exposure during development, and in varying scale.

I must remember to change the setting back when shooting video. Or the video will be overblown and, AFAIK, there is no way to fix that.

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Apr 27, 2015permalink

mpgxsvcd

I agree with everything you said for short exposure photography but what about long exposure photography like astrophotography(Several minutes or more)? There longer exposures increases the electrical read noise and decreases the shot noise because the signal is more consistent over the longer period of time.

It would be interesting to find the shutter duration at which shot noise is surpassed by electrical read noise in particular cameras.

In addition stacking light exposures along with dark frames can reduce the shot and read noise by using some form of averaging with multiple frames. Since the noise is random the difference between each frame is the “unwanted signal”.

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Apr 27, 2015permalink

mpgxsvcd

Do our eyes see noise? Let your eyes adjust to a dark moonless night sky one night. Then look up and gaze into the starlit blackness. I swear you can see what looks like noise in the sky. It is probably fluctuations due to transparency and seeing conditions but it resembles shot noise that we see in short exposure night time images.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

Heat and the effects of image stacking are two good points. I'll see if they can be incorporated into part 2.

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Apr 27, 2015permalink

mpgxsvcd

Thanks. Stacking has always been something that puzzled and intrigued me at the same time.

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Apr 27, 2015permalink

Rishi Sanyal

Rishi Sanyal

"There longer exposures increases the electrical read noise and decreases the shot noise because the signal is more consistent over the longer period of time."

The shot noise is not necessarily decreased simply by longer exposures, b/c remember - it's the total amount of light that is captured that matters. In astrophotography, there's so little light to begin with that you're using long exposures just to get more signal (and increase SNR by decreasing shot noise contributions).

But you're right about thermal noise becoming an issue - its proportion becomes larger b/c of the really, really long exposures. At that point, it can start becoming a relatively significant source of noise. This is a very special case, though, perhaps even too special to be addressed in part II...

And, yes, I know what you mean about the noise you start seeing when it's really dark. I bet there's a huge physiological component to that though.

And, yes, averaging n images increases SNR by sqrt(n).

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Apr 28, 2015permalink

mpgxsvcd

Have you ever done any astrophotography Rishi? I think you would really enjoy it if you haven't. You can get a great setup for about $1500 if you choose the components with a budget in mind.

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Apr 28, 2015permalink

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retro76

It's funny I used to be a canon shooter who was all about the silky smooth noise free look, but recently I have become a Nikon guy who is starting to love the "feel" noise adds to an image. I can't quantify it, but sometimes the smooth look is a bit too clinical, great for the studio, but for everything else noise is rather lovely and gives that beautiful journalistic look IMHO. In fact it's reason #35 why the sensor doesn't matter in an age where people will shoot a $3000 camera simply to run the images through VSCO and destroy the data just to emulate all the imperfections (which I love) of film.

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Apr 27, 2015*permalink

Roadrunnerdeluxe

Excellent article, thank you! I started to blame my camera for noisy low light shots...might be user error after all ; )

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Apr 27, 2015permalink

mpgxsvcd

Richard,

Thank you. Simply, Thank you. That was a brilliant article. More like this please if you can find the time.

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Apr 27, 2015*permalink

Mssimo

Mssimo

On the D810, i use the flat profile (with ADR might even be better). This gives more accurate view of clipping. Most prographers use standard or even worse vivid. This will lead you to underexposing images by 1-2 stops.

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Apr 27, 2015permalink

thk0

"There are three factors that affect how much light is available for your sensor to capture: your shutter speed, the size of your aperture (not f-number) and the size of your sensor."

Yes, f-number. If you use the physical aperture size, then the sensor size does not matter (assuming the same sensor coverage of the light circle). The amount of light passing through the lens, and hence "available for your sensor", only depends on the area of the entrance pupil, transmission efficiency and the duration of the exposure. If you use f-number, then the physical aperture scales with the sensor size and sensor size becomes part of the equation.

(edits for typos)

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Apr 27, 2015*permalink

Andy C Knight

I was thinking along the same lines

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Apr 27, 2015permalink

Androole

Yep, exactly. Since an Voigtlander 25mm f0.95 lens has the same physical aperture size as a 50mm f1.9 lens, it passes the same amount of total light despite shining on a sensor 1/4 the size. Hence, equivalence!

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Apr 27, 2015permalink

nutraman

oh yeah, well I shoot without a lens. ;)

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Apr 27, 2015permalink

dosdan

"There are three factors that affect how much light is available for your sensor to capture: your shutter speed, the size of your aperture (not f-number) and the size of your sensor."

The "Exposure Triangle" is Shutter Speed, F/number, Scene Luminance. That's why you use a flash or a light reflecting panel: to increase the scene luminance component of exposure. These 3 determine the exposure (the photonic density captured per mm2 during the exposure period). So if these 3 remain the same, with larger sensors you get the same exposure, but more Total Light (more photons) being captured. For the same exposure, there's more photons collected, so there's also more shot noise photons in a bigger sensor capture. But, since the Shot Noise SNR is proportional to the sq root of the number of photons, it's still better with a bigger sensor.

Example. Small sensor: 10,000 photons captured, SNR = 10,000/100= 100:1

2.3x bigger sensor: 23,000 photons captured: SNR = 23,000/151.7 = 151.7:1

Dan

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Apr 27, 2015*permalink

dosdan

Another way of stating this: At the same exposure level and similar sensor technology, the shot noise SNR is proportional to the sq root of the sensor area. So 4x bigger sensor = 2x better shot noise SNR.

Dan.

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Apr 27, 2015*permalink

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Discovery Of Light

Discovery Of Light

Interesting I think about shot noise but not as much as read noise. I guess I will start making that part of the routine. I have the old 7d and it's a noisy bugger for interiors especially when I am trying keep window light from blowing out. The way I get around that is to shoot a 3 shot bracket at low ISO and then average it PS. The noise mostly goes away and I end up with a bit more dynamic range. Ghosting is always a concern though. At some point I would love to get away from all that tedious post processing.

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Apr 27, 2015permalink

www_zeeshan_de

Thank you for the posting. Thats why the i dont use APS-C Sensor toys anymore. Using a full frame Sony A99 i fix it to ISO100 and take pictures with EV+1,3 just to exposure the sensr CORRECTLY. After that i get pictures from RAW Files on which there is NO REQUIREMENT of denoising at all.

For more Info have a look at my german page at:

http://www.zeeshan.de/fotografie_apsc_vs_vollformat/0_slta99.htm

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Apr 27, 2015permalink

b craw

b craw

And yet I am compelled to state that many photographers' work would be improved greatly if they were to play more with 'toys'.

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Apr 27, 2015permalink

Androole

Somewhat ironic that you call APS-C cameras toys, but use a 3 year old SLT FF camera with ISO performance and dynamic range...almost exactly the same as a APS-C D5500!

http://www.dxomark.com/Cameras/Compare/Side-by-side/Nikon-D5500-versus-Sony-SLT-Alpha-99___998_831

log2(1555)-log2(1458) = 0.09.

So hey, I guess you've got 1/11th of an EV better performance than that toy?

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Apr 27, 2015permalink

Andy Crowe

Full Frame? That's tiny! http://youtube.com/watch?v=PHYidejT3KY :)

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Apr 27, 2015permalink

RichRMA

That's a key thing, if you no longer have to waste time denoising, then the use of FF could be justified if your work generates income, or you just want to save time. Now, if only the mfgs would leave the silly 3:2 format that wastes part of the lens image circle and forces most photogs to crop away part of the sides.

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Apr 27, 2015permalink

Androole

Yeah, wouldn't it be great to have a 4:3 or 1:1 (30.5 x 30.5!) FF sensor that used the same old lenses?

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Apr 27, 2015permalink

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digiart

Very informative article. It explains very well what we know from experience. Thank you!

P.S.

It would be excellent if in the reviews DPR tested each camera to find out what is the ISO setting that gives you the best dynamic range.

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Apr 27, 2015permalink

feraudy

The best dynamic range is generally the lowest ISO (but not quite always, sometimes it's the second lowest).

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Apr 27, 2015permalink

digiart

@feraudy,

Because it's not always the lowest ISO setting, that is why testing (and sharing) that info in the reviews would be valuable.

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Apr 28, 2015permalink

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Iliah Borg

> your camera's exposure meter and exposure guides are all based around correctly exposing the midtones of JPEGs

I would use "correct placement on the brightness scale" maybe instead of "exposing". Technically, the current fashion for tone reproduction is like this: start the shoulder at L*≈70, but place the skin tone (L*≈65) where it belongs - that is, the accurate reproduction starts at skin tone, which is higher than midtone.

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Apr 27, 2015*permalink

Richard Butler

Richard Butler

Wouldn't that be more of a decision about the shape of the tone-curve? My understanding was that the ISO standard is (rather loosely) based on representation of mid-tones.

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Apr 27, 2015permalink

Iliah Borg

I'm trying to say that "correctly exposed" is in fact "correct brightness".

Yes, ISO standard insists on 118 on sRGB scale for midtone placement.

Out of necessity, all generic tone curves need to work with rated ISO so as to place skin tone (starting at L* close to 70, with the "darker than light" being 67) close to where it belongs.

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Apr 27, 2015*permalink

zjo

hi

can you elaborate on that a little please?

do you mean that jpeg tone curve usually leaves skintones unaltered?

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Apr 27, 2015permalink

Iliah Borg

Tone means brightness here. Any sane generic tone curve is designed in such a way, that "correct exposure" results in skin brightness being as it is expected.

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Apr 27, 2015*permalink

Richard Butler

Richard Butler

Does this work better, do you think:

'The other downside is that, because your camera's exposure meter and exposure guides are all based around putting scene midtones at the correct JPEG brightness level, they're not as helpful as they could be for assessing when you your Raw file has been correctly exposed to the right.'

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Apr 27, 2015permalink

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Pritzl

First sentence made me want to clap. However, I get the impression some of the rest of the article was a bit rushed?

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Apr 27, 2015permalink

AbrasiveReducer

The problem with pouring on exposure without clipping the highlights is just that. It's great when you have your D800 on a tripod, mirror locked up, and are meticulously focusing your Zeiss lens. You are crafting the perfect image.

In practice, when doing anything where time is not unlimited, setting the camera to just touch the right without going over will result in the exposure going over, and clipping. At least that's been my experience. Better to expose less and if unavoidable, pull up noisy shadows than try to recover highlights that don't exist.

Of course, I grew up with film, where 400 ASA was fast so I don't use incredibly high ISOs since they're too noisy.

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Apr 27, 2015permalink

Thematic

Thematic

Not a good way to shoot if quality images are your end goal.

Please read this:

http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf

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Apr 27, 2015permalink

Richard Schumer

"Of course, I grew up with film, where 400 ASA was fast so I don't use incredibly high ISOs since they're too noisy."

I grew up on film, too. After reading A. Adam's Zone system, I used its technique for exposing for shadows and developing for highlights, and found "Pushing" did not affect Zone 1, the deepest shadows. Using 135 film, it was not usually practical to change development times for the highlights so I used an incident light meter and changed the hardness of the printing paper for highlight adjustment.

The analogue to this in the digital world means I have to find where Zone 7 or 8 is on the sensor thru some tests and then set my incident meter to a "speed" that will not oversaturate the sensor; I expect to adjust the shadows in PP. Perhaps I will have to mask the shadows and run heavy noise reduction on them; if so, so be it.

Just thinking aloud.

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Apr 27, 2015permalink

RichRMA

Adams had his zone system and some followed it, but reading old photogs books, you get the sense that most of them didn't worry about capturing detail in the entire scene and made a choice to block shadows or blow highlights in order to capture correctly the rest of the image.

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Apr 27, 2015permalink

Richard Schumer

@ RichRMA -- You're right; digital changes it all, though. Now my goal is to capture as much information (data) as possible and bring out what I choose in PP rather than to limit myself to the traditional 8 EVs film could capture with rolloffs at the top and bottom.

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Apr 27, 2015permalink

graybalanced

The concerns about clipping are to some extent (pardon the pun) overblown. I've read that the histogram and clipping on most camera LCDs is calculated based on sRGB unless you have changed it to Adobe RGB, which means the histogram on many cameras is conservative either way. This has been true in my experience. If a highlight looks a tiny bit clipped in camera, chances are it is not clipped at all when looking at the raw data in the raw processor.

I agree that to be on the safe side it's a good idea to back off from obvious clipping, but I don't think it's necessary to back off very much because you then start wasting the valuable high bits, which I hope DPReview will talk about in the second article.

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Apr 27, 2015permalink

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ThrowFirewoodAtMe

ThrowFirewoodAtMe

Very nice! One of your best articles. I now know why I have had a habit for ETTR in the past. Especially on my 6D which "underexposes" a little even with spot metering.

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Apr 27, 2015permalink

naththo

What about the sensor heating issue problem especially in Pentax and Sony Mirrorless? That would have increase noise significantly especially Australia is a hot country not a cold country at all.

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Apr 27, 2015permalink

digiart

I think it will be discussed in part 2. IMO this can be an issue in dim lit scenes when using Live View or right after using Live View for some time. Not tested though.

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Apr 27, 2015permalink

RichRMA

And it can be considerable. Shoot on a hot day, especially if you have a black plastic camera body which heats up more than metal, and noise can (arbitrarily) be double that of shooting on a cold day.

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Apr 27, 2015permalink

naththo

Yup pretty much so RichRMA. Thats why my friend who has Pentax and wants to take astro photos but he had to custom build the cooler system for that Pentax as he lives in Mackay which is in tropical region so the heat is constant almost all year round with rather high humidity. Having custom built cooling system it helps a lot for astro photos.

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Apr 28, 2015permalink

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b craw

b craw

You make no mention of the third type of noise - the one with the most potential to harm image(s): DPR reader commentary.

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Apr 27, 2015permalink

zsedcft

Horshack beat you to this joke.

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Apr 27, 2015permalink

b craw

b craw

That is a pity, but I'll survive. :)

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Apr 27, 2015permalink

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Gregm61

Nice article. Thanks, now for the fun part. Reading the geek responses to get even more technical because they can't help themselves...

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Apr 27, 2015permalink

(unknown member)

I've always exposed to the right, but no matter what people say, even with the blinkies on it's easy to blow some highlights, so my exposures have slowly moved a little left, and the modest increase in noise just does not matter. Digital sensors are much better at capturing shadow detail than retaining highlight detail.

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Apr 27, 2015permalink

zsedcft

I'm the same. Sensor technology has come so far in the last 10 years that making exposure decisions because of the sensor is a much smaller thing than it used to be.

Blown highlights are far more offensive to me than shadow noise so I usually expose to the middle now. You can always recover a shadow (at the expense of some noise) but a blown highlight is gone forever.

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Apr 27, 2015permalink

RichRMA

Which is why most cameras today have live histograms. More should use them.

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Apr 27, 2015permalink

(unknown member)

Live histograms tend to be less accurate than the blinkies, at least on my camera. But it all depends on the subject. When I shoot faces, I usually want to expose for the face and let the highlights blow if needed. With nice side light into trees, I'll underexpose a little, knowing that the camera will not be right about the highlights in the raw file even in my EVF.

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Apr 27, 2015permalink

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samdim

Thank you DPR for a very intresting article

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Apr 27, 2015permalink

zsedcft

I was under the impression that ETTR is often not a good idea. If the subject is the brightest thing in the scene (a wedding dress or clouds for example) exposing to have the wedding dress almost clipping is a bad idea. The closer you get to clipping the less tones you have available for highlights. I use ETTR on my eos-m for timelapses, but I avoid the very top of the histogram when I am actually holding the camera. It may not happen as much with 14/16bit RAW files, but I believe it is still an issue.

(if you can afford it) Just get a D800/D800E/D810/A7R and you will have a camera that you can shoot at ISO 100 and recover everything in post processing. I have found that ISO 100 with the exposure pushed in lightroom looks the same as ISO 1600 from the camera. Shadow noise is always better than blown highlights IMO so I usually pretty conservative with exposure. If you want the best of both worlds in landscape, just shoot a exposure bracket and pick the best or blend them.

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Apr 27, 2015permalink

Iliah Borg

For ETTR to work well, the clipping point needs to be within 3% from linear response; the in-camera raw data compression (if lossy) needs to be independent of the raw values; and the converter needs to apply compensations of exposure in a linear fashion.

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Apr 27, 2015permalink

Thematic

Thematic

you are indeed wrong and dpreview is right

what you are doing is introducing posterization into your images and reducing image quality.

ETTR is a "shift" in exposure, not clipping highlights. Underexposure is the enemy of a digital sensor.

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Apr 27, 2015*permalink

zsedcft

Not as much posterization as you will get when you have 5 seconds to take a once-in-a-lifetime photo and you overexpose it.

I am not saying that this will often happen, but for it to even happen once is totally unacceptable to me. If you have enough time to review a picture on the LCD then surely you have enough time to shoot a 5 shot bracket to ensure that you have a perfect exposure.

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Apr 27, 2015permalink

Thematic

Thematic

bracketing is different - you are right about that

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Apr 27, 2015permalink

RichRMA

I found that doing that sucks the color from an image, (kind of like how Foveon sensors render high ISO), worse than if you shoot at the tone and DR restricted 1600 ISO. But that was one camera, you're results are obviously different.

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Apr 27, 2015permalink

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Dennis

Richard, great article. If you find time, at some point, to elaborate on a couple points, the illustration showing the test tubes makes it clear that SNR increases with exposure time, but doesn't address the confusion some people have with photosite size; if you have a 16MP and 24MP sensor, both are the same size, but each photosite on the 24MP sensor sees fewer photons and should therefore have more visible noise. There's no explanation of the difference between the 100% view and the downsampled or printed view. Therefore, when you say:

> And, since we've established that capturing more light improves your signal-to-noise ratio

I'm not sure you got there; you've explained how an increase in exposure increases the SNR, but without talking about averaging, you could argue that 36million (FF) photosites versus 16million (APS-C) should have the same noise (same test tube size, after all).

- Dennis

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Apr 27, 2015permalink

J A C S

J A C S

Talking about pixel size would just complicate the article. A simple remark that the noise needs to be evaluated at the same size and is mostly independent of the pixel size would help but going too deeply into that would change the focus. Also, QE could have been mentioned with a remark that it does not make much difference for sensors of the same generation.

I believe that the purpose of the article is to emphasize on shot noise as a function of the total light and is aimed at beginners. For a more technical exposition, see http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/

for example.

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Apr 27, 2015permalink

Richard Butler

Richard Butler

J A C S is right that I was trying to keep the article accessible, but I'll see if I can find a way to clarify these issues.

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Apr 27, 2015permalink

Dennis

I agree with keeping it easy for everyone to understand; I've just seen enough debates in the forums over this ... people who insist that FF is "cleaner" than APS-C because the pixels are bigger ...

Just a thought, and thanks for considering it.

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Apr 27, 2015permalink

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Horshack

I use ETTR extensively on my original 5D bodies. Due to JPEG histogram issues mentioned in the article I recommend that everyone calibrate their camera's raw highlight clipping by shooting typical scenes with varying overexposure and then processing the images in their preferred app to see correlate actual clipping to what they see on the histogram. Another method is with Iliah Borg and Co. RawDigger app; there's a great 3-part article on this here: http://www.rawdigger.com/howtouse/rawdigger-histograms-what-is-the-raw-histogram.

My field ETTR metering technique is to leave the camera on spot metering. I meter the brightest highlight I want retained, which puts that highlight at middle grey, then dial in an exposure +2EV to +3EV above that depend on the reflectivity of scene and the camera I'm using.

Here are some 5D ETTR examples (before+after):

http://horshack.smugmug.com/photos/i-NXkhBhH/0/O/i-NXkhBhH.png

http://horshack.smugmug.com/photos/i-zhPzj4M/0/O/i-zhPzj4M.png

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Apr 27, 2015permalink

zsedcft

I love your first picture. Did you burn out the top and bottom or use some lightroom graduated filters?

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Apr 27, 2015permalink

RichRMA

Yet another explanation of ETTR:

http://www.cambridgeincolour.com/tutorials/digital-exposure-techniques.htm

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Apr 27, 2015permalink

Horshack

Thanks zsedcft. I used a combination of LR digital GND and local adjustments. For me the biggest benefit of ETTR is not lower noise per se but greater flexibility in applying contrast in post. Extreme contrast adjustments can sometimes yield more visible noise than directly raising shadows.

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Apr 27, 2015permalink

audiobomber

audiobomber

Horshack, your samples are definitely worth 1000 words in explaining ETTR. I will give it a try.

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Apr 28, 2015permalink

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EskeRahn

EskeRahn

Nice article.

Have a look at this also for some formulas

http://www.diskusjon.no/index.php?showtopic=1024832

Yes it is in Danish, but the formulas should be easy to get none the less.

The main points

1) Thermal noise (fixed sensor size)

Relative noise goes ad 1/d, √N and √T , (N number of Mpixels, d aperture diameter)

(T in Kelvin, ie °C+273.15)

2) Rayleigh's criteria and sensor width.

F * √N < W , (N number of Mpixels, W in mm, red light, F aperture)

(It is a numeric coincidence that the constants cancels out, see link for calculus)

(Point 3 is too pessimistic, and I ought to edit that, for most it is about 1/12000 of viewing distance)

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Apr 27, 2015*permalink

junk1

Have manufacturers confirmed that signal levels (pixel size) are so low that randomness in the number of photons is noticeable?

I've always thought of larger sensors as capturing a larger signal, therefore hiding the electronic noise (and any other sources of noise), but how do we prove where the noise comes from (shot versus electronic).

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Apr 27, 2015*permalink

junk1

OK...so if the A/D convertors, amplifiers; etc are a small source of noise, then we need more sensitive sensors - higher rate of conversion of protons to electrons (which is always a good thing!).

Similar electronics are used for so many things such as radar which needs very low noise, so I can agree that those items are probably "mature" and hard to improve upon.

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Apr 27, 2015permalink

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Andy C Knight

I'm having difficulty understanding this line...

"There are three factors that affect how much light is available for your sensor to capture: your shutter speed, the size of your aperture (not f-number) and the size of your sensor."

I keep thinking... Shutter, F number & sensor size or...

Shutter, physical aperture size & focal length.

Can someone explain where I am going wrong?

Regards

Andy.

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Apr 27, 2015permalink

junk1

Shutter speed and f-stop (aperture) control how much light/photons gets through the aperture during the capture.

If the camera has a larger sensor with larger pixels, more light hits each pixel, so there's a larger signal output from each pixel.

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Apr 27, 2015permalink

Andy C Knight

Ok...

But why is it Shutter, Physical aperture size & sensor size...

and not (say) Shutter, F number & sensor size??

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Apr 27, 2015permalink

junk1

F number is basically the shutter size - the size of the opening.

For a given sensor, the F-stop is proportional to the square root of the amount of light that will go through.

What I mean is:

2.8 x 2.8 = 8.

4 x 4 = 16, so double the brightness/intensity.

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Apr 27, 2015*permalink

J A C S

J A C S

It depends on the context. If the lens and the apertures are the same, shrinking the sensor shrinks the total light. If they are equivalent (like 100/4 on FF vs. 50/2 on m43), the size of the apertures are the same; the total light is the same but the sensor sizes are different.

I would say that it depends on the SS and on the equivalent aperture (and on vignetting, transmission, etc. but those are better left out for the purpose of this article) . One can even give a formula, similar to the one for the EV.

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Apr 27, 2015permalink

EXX

EXX

The issue is that smaller sensors use lenses with shorter focal lengths to obtain a proper field of view, e.g. 50mm on full frame, 35 mm on APS-C and 12 mm on 2/3" sensors give the same field of view. The aperture has the focal length in the formula: A = focal length/f-stop number. So, using the same f-stop, the shorter the focal length, the smaller the aperture.

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Apr 27, 2015permalink

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JEROME NOLAS

Can you explain in two sentences, it's too long... :)

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Apr 27, 2015permalink

Richard Butler

Richard Butler

The main source of noise comes from the light you capture: not your camera. The more light you can capture, the less you'll notice the noise.

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Apr 27, 2015permalink

Report

JEROME NOLAS

Thanks!

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Apr 27, 2015permalink

LensBeginner

LensBeginner

Nice summary! :-)

I read it all, however, and it was definitely worth it.

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Apr 27, 2015permalink

Table of Contents

What's that noise? Part one: Shedding some light on the sources of noise

Sources of camera noise part two: Electronic Noise