Noise and ISO, One more thread

[Great Bustard]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light signal"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

It say's "amplifying the light signal", not "amplifying the light.

Apologies -- that's what I meant -- typo. I fixed it above.

Big difference.

OK, so back to my questions. What are the answers?

The actual question is how a reader interprets the phrase. My little experiment shows that it is interpreted as light amplification. Thus, Bob is right, and he didn't invent the misconception.

OK, so I went back to the top and read through. I get what you're saying. Bob said:

The root of the ISO fallacy is viewing photography as 'light in-light out'. Then, the thinking goes, to make a dark image 'brighter' you need 'more light', so the light needs to be 'amplified', hence 'gain'. In fact the output is just a number, representing a position in a grey scale. It takes no more light energy to write 0, 10, 100 or any other number you want.

which is correct. Porky (alfn) replied:

Nobody in their right mind thinks that. You are attributing a misconception that does not exist to your critics and then attacking them for it, which is very disingenuous.

Then you said:

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

where the second paragraph was a quote from the article (but you didn't put it in italics, so that's what confused me -- I didn't realize it was a quote from the article) as a counterexample to Porky's claim that "no one in their right mind thinks that".

Gotcha!

 

[fferreres]

The job of ISO is merely to amplify the light signal that the camera receives.

No. The job of the ISO setting is to control how large a digital number is stored in the camera's JPEG output for a given number of photons captured by a sensor element.

Funny, I move the ISO setting in A-Mode and I see that right after changing the ISO, the shutter also changes. I guess In need to go back and take classes with you, should you accept me as your pupil, which is highly improbable.

 

[Great Bustard]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true.

You are saying the author of the BS above is wrong. Yes, he is. The quote supports Bob's point, that is that the misconception does exist.

Apologies for not being more clear -- I wasn't responding to the contents of the link (didn't read it) -- I was responding to the comment "The job of ISO is merely to amplify the light signal that the camera receives". That's simply not true.

Yes, and it's from the link, a quote. Verbatim.

That was my disconnect. Hopefully, my post above correctly summarizes the situation.

 

[FingerPainter]

The job of ISO is merely to amplify the light signal that the camera receives.

No. The job of the ISO setting is to control how large a digital number is stored in the camera's JPEG output for a given number of photons captured by a sensor element.

Funny, I move the ISO setting in A-Mode and I see that right after changing the ISO, the shutter also changes.

That's the autoexposure system at work, not the ISO on its own.

I guess In need to go back and take classes with you, should you accept me as your pupil, which is highly improbable.

Improbable for geographic reasons, perhaps.

 

[Xasan]

Raising the ISO increases the amplification of the voltage the photons generate on each sensor pixel.

Photons generate charge. Raising ISO doesn't necessarily increases the amplification of the voltage. In fact, ISO has nothing to do with amplification or gain. Any photographic speed standard is always about points on H&D curve which exists for fully processed image and mapping exposure to output - be it density, transparency, or data numbers.

Only for black and white film development is sometimes referred to as amplification, that's chemical amplification to get from invisible latent silver image with effectively zero optical density to visible silver image with meaningful density.

Once the shutter closes, the number of photos doesn't change.

There are 2 sources of noise in an image:

1. Shot noise - noise inherent in the light coming from the scene.

2. Read noise -

a) Front End Read Noise - noise introduced by the camera itself; heat, camera electronics prior to the voltage being amplified.

b) Back End Read Noise - additional noise some cameras introduce when the voltage is converted to a digital value.

Shot noise is the result of low levels of light hitting the sensor.

Both the effects of shot noise and read noise are included in the pixel's final digital value.

Now, when you raise the ISO in camera only the shot noise and Front End Read Noise are amplified when the voltage is amplified. The Back End Read Noise, if any, is introduced after the voltage has been amplified and during its conversion to a digital value.

If you raise the "exposure" in a raw converter you are essentially just multiplying the final digital value for each pixel which will include Shot Noise, Front End Read Noise and any Back End Read Noise.

Unless you are fully aware of the camera's noise properties (whether it introduces back end read noise or not), to minimise noise in the final image you are better off raising the ISO in camera (assuming you cannot widen the aperture and/or slow the shutter because of DOF, motion blur constraints) than shooting with a lower ISO in camera and increasing the image lightness in post because raising the ISO results in only the Shot Noise and Front End read Noise being amplified. In PP, raising the "exposure" results in the Shot Noise, Front End Read Noise AND Back End Read Noise being amplified.

 

[David1961]

Raising the ISO increases the amplification of the voltage the photons generate on each sensor pixel.

Photons generate charge. Raising ISO doesn't necessarily increases the amplification of the voltage. In fact, ISO has nothing to do with amplification or gain. Any photographic speed standard is always about points on H&D curve which exists for fully processed image and mapping exposure to output - be it density, transparency, or data numbers.

Only for black and white film development is sometimes referred to as amplification, that's chemical amplification to get from invisible latent silver image with effectively zero optical density to visible silver image with meaningful density.

jrtrent, post: 63354351, member: 1728254"]
Perhaps each camera is different. With mine, images shot any higher than ISO 400 are going to be unacceptably noisy to me, and images shot at ISO 200 (my camera's lowest setting) have more clipped highlights than those shot at ISO 400, so my camera stays at ISO 400 all the time. In light too dim for handheld exposures at that ISO, I either mount a flash or put the camera away. Following this procedure, noise is never an issue, and I never have to think about ISO.

I'm sure they are.

But what was beaten into my head was that raising the ISO does NOT Raise the sensitivity of the sensor.

that part is correct

What it does is increase the amplification of the photons that the sensor receives.

That part is incorrect. What gets amplified is the electrical signal from the sensor, not the photons.

 

[bobn2]

Perhaps each camera is different. With mine, images shot any higher than ISO 400 are going to be unacceptably noisy to me, and images shot at ISO 200 (my camera's lowest setting) have more clipped highlights than those shot at ISO 400, so my camera stays at ISO 400 all the time. In light too dim for handheld exposures at that ISO, I either mount a flash or put the camera away. Following this procedure, noise is never an issue, and I never have to think about ISO.

I'm sure they are.

But what was beaten into my head was that raising the ISO does NOT Raise the sensitivity of the sensor. What it does is increase the amplification of the photons that the sensor receives.

Photons can't be amplified.

And you don't need to amplify them. All you need to do is specify is how the number of photons captured should be translated into tones in the final image. That has nothing to do with gain.

The root of the ISO fallacy is viewing photography as 'light in-light out'. Then, the thinking goes, to make a dark image 'brighter' you need 'more light', so the light needs to be 'amplified', hence 'gain'.

Nobody in their right mind thinks that. You are attributing a misconception that does not exist to your critics and then attacking them for it, which is very disingenuous.

Talking of disingenuous, I said nothing whatsoever of my 'critics', nor did I attack anyone. The only person doing attacking here would be you....

Anyway, Xasan has given you a very good example of a 'tutorial', no less based on that very same thinking. Whatever you choose to say, the line of thinking I describe is very common. I describe it not to do down those who have unfortunately been misled by the raft of bad information on this subject, just to help people understand what are the roots of the misconception.

--
...because you know, sometimes words have two meanings.

 

[bobn2]

Nope. Photons are quanta, they can't be amplified.

But the A>D signal can be amplified. The photons create the charge, the digital conversion creates a number, which can be multiplied.

Sure, but that 'amplification' (nor the multiplication of the number, which is technically a better way of doing it) changes the number of photons, and the number of photons is what determines the noise properties of the photo. It's not that gain doesn't happen that's the problem, it's the misidentification of 'gain' as being what 'ISO' is essentially doing.

 

[bobn2]

Perhaps each camera is different. With mine, images shot any higher than ISO 400 are going to be unacceptably noisy to me, and images shot at ISO 200 (my camera's lowest setting) have more clipped highlights than those shot at ISO 400, so my camera stays at ISO 400 all the time. In light too dim for handheld exposures at that ISO, I either mount a flash or put the camera away. Following this procedure, noise is never an issue, and I never have to think about ISO.

I'm sure they are.

But what was beaten into my head was that raising the ISO does NOT Raise the sensitivity of the sensor. What it does is increase the amplification of the photons that the sensor receives.

Nope. Photons are quanta, they can't be amplified. It's actually quite an important point, because in the main noise is determined by the number of photons captured. The voltage output of the sensor represents that number of photons. Amplifying it doesn't change the number of photons, it just changes the 'exchange rate'.

The whole identification of ISO with gain is bogus. Unfortunately, it's also a brainworm. Once people adopt the idea, it's really hard to get rid of it.

At this point I'll be happy to accept any technical explanation. But isn't what you say above, for all practical purposes the same thing?

I don't think it is. The key point is when (if) 'amplification' occurs, it doesn't change either the number of photons or the energy of the photons, so saying that 'photons' have been amplified really is just plain wrong. What matters so far as noise is concerned is the number of photons,. The size of the signal that represents that number really is immaterial apart from the electronic optimisation of the capture chain for a particular exposure level.

 

[bobn2]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

It say's "amplifying the light signal", not "amplifying the light.

Big difference.

Try to explain that difference. What do you mean by 'signal'. What does the 'signal' represent?

 

[bobn2]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

It say's "amplifying the light signal", not "amplifying the light.

Big difference.

99.9999% (or 99,9999% if not American) of cases the discussion arises as a discussion of what happens where.

In G.B. the only thing common to all photos is the average light intensity we see in the final recorded (or observed) photo. The all seem to have the same amount of light intensity or "lightness" in terms of Church of No Triangle credo.

'Light intensity' and 'lightness' are completely different things. Lightness is a perceptual measure, it locates a tone on a grey scale running from perceptual 'black' to perceptual 'white'. You can describe paint in terms of lightness, its very hard to do so with light intensity. The misidentification of lightness with light intensity is the heart of the 'light in-light out' fallacy, which Porky believes doesn't exist. The fact that that fallacy is embedded right in the middle of the 'triangle' is one of the many reasons it's a very poor teaching aid, and its use in general results in learners adopting multiple misconceptions. Not their fault - bad teaching.

 

[mamallama]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

It say's "amplifying the light signal", not "amplifying the light.

Big difference.

Best not get into a word war with our forum experts. They will wordsmith you to death. They think only they know the right words for everything.

 

[bobn2]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

It say's "amplifying the light signal", not "amplifying the light.

Big difference.

Best not get into a word war with our forum experts. They will wordsmith you to death. They think only they know the right words for everything.

The 'war' is one of understanding, not words. The reason for discussing words is that use of words impacts cognition (read a bit of Chomsky), and in particular using different words for different concepts helps the mind delineate those different concepts. Use the same word for different concepts and it's really hard to keep your thought processes straight. In a discussion, it's a good idea if there's some agreement on what the words mean in that context. You have every right to adopt your own meanings, but don't be surprised if it results in talking at cross purposes. In a field such as photography, a formal vocabulary has been established for many of the key words. It's not unreasonable to conduct a discussion on the basis of that vocabulary.

In the case above. PhotoFactor obviously believes that the addition of the word 'signal' makes a big change to the meaning of the sentence. That's fine, but it appears not to be evident to others in the discussion, so If he wants them to take what he says on board he needs now to explain why that word makes a substantive difference.

 

[mamallama]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

It say's "amplifying the light signal", not "amplifying the light.

Big difference.

Best not get into a word war with our forum experts. They will wordsmith you to death. They think only they know the right words for everything.

The 'war' is one of understanding, not words. The reason for discussing words is that use of words impacts cognition (read a bit of Chomsky), and in particular using different words for different concepts helps the mind delineate those different concepts. Use the same word for different concepts and it's really hard to keep your thought processes straight. In a discussion, it's a good idea if there's some agreement on what the words mean in that context. You have every right to adopt your own meanings, but don't be surprised if it results in talking at cross purposes. In a field such as photography, a formal vocabulary has been established for many of the key words. It's not unreasonable to conduct a discussion on the basis of that vocabulary.

In the case above. PhotoFactor obviously believes that the addition of the word 'signal' makes a big change to the meaning of the sentence. That's fine, but it appears not to be evident to others in the discussion, so If he wants them to take what he says on board he needs now to explain why that word makes a substantive difference.

If you are trying to make this forum like a technical journal you need to be more careful with your words. In the meantime you are just nitpicking others with a lot of word misuse yourself.

 

[David1961]

That's fine, but it appears not to be evident to others in the discussion...

I see your comment as simply your opinion and not an established fact.

It say's "amplifying the light signal", not "amplifying the light."

My interpretation is that there is a huge difference in the two meanings.

"amplifying the light signal " to me clearly means the signal from the sensor pixel generated by the light.

"amplifying the light." to me clearly means amplifying the light itself.

 

[David1961]

In a field such as photography, a formal vocabulary has been established for many of the key words. It's not unreasonable to conduct a discussion on the basis of that vocabulary.

Yes but people also need to balance the vocabulary they use so that it is not too technical for the intended audience. Obviously that is much harder in online forums like this.

I'm sure if someone asks a surgeon how to perform a particular operation the surgeon could make the explanation virtually incomprehensible to the average layman with highly technical words in the medical vocabulary or they could make it fairly simple to understand at least the basics using much more commonly used words.

People in online forums trying to portray themselves as being highly knowledgeable in a particular field by using verbose language with unnecessary technical terms more often than not leave themselves open to being thought of as egotistical and/or narcissistic, especially when the information they post is incorrect.

 

[mamallama]

That's fine, but it appears not to be evident to others in the discussion...

I see your comment as simply your opinion and not an established fact.

It say's "amplifying the light signal", not "amplifying the light."

My interpretation is that there is a huge difference in the two meanings.

"amplifying the light signal " to me clearly means the signal from the sensor pixel generated by the light.

"amplifying the light." to me clearly means amplifying the light itself.

Signal is a perfectly good English word to clarify what he meant. A definition of signal in the English language is "a detectable physical quantity or impulse like voltage, current or magnetic field".

Anyone who understands English would understand his clarification. Don't let the nitpickers drag you down.

 

[David1961]

That's fine, but it appears not to be evident to others in the discussion...

I see your comment as simply your opinion and not an established fact.

It say's "amplifying the light _signal_", _not "amplifying the light."_

My interpretation is that there is a huge difference in the two meanings.

"amplifying the light signal " to me clearly means the signal from the sensor pixel generated by the light.

"amplifying the light." to me clearly means amplifying the light itself.

Signal is a perfectly good English word to clarify what he meant. A definition of signal in the English language is "a detectable physical quantity or impulse like voltage, current or magnetic field".

Anyone who understands English would understand his clarification. Don't let the nitpickers drag you down.

That is exactly the point I was making

To me at least, the huge difference in the two meanings is very obvious.

 

[D Cox]

You are attributing a misconception that does not exist

You will need Houdini-level skills to explain the following differently from the misconception Bob describes (taken from https://www.colesclassroom.com/understanding-iso )

The job of ISO is merely to amplify the light signal that the camera receives. In the process, it can produce a similar effect as opening the aperture or using a slow shutter speed.

Not even remotely true. Tell me, aside from lightness, what do the following photos have in common, and what is different, if photos are taken of the same scene with the same camera and lens:

1. f/2.8 1/200 ISO 100
2. f/5.6 1/200 ISO 400
3. f/2.8 1/800 ISO 400
4. f/5.6 1/800 ISO 1600

In what way is the ISO setting "amplifying the light"? In what way does it "produce a similar effect as opening the aperture or using a slow shutter speed"? Aside, of course, from resulting in photos with the same lightness.

I think of ISO settings above 100 as "ameliorated underexposure".

The usual reason a photographer may want to underexpose is to be able to use a faster shutter speed. For instance, your No. 3 is two stops less exposure than No.1, with a faster speed (or shorter time).

Sometimes one may underexpose to be able to increase depth of field.

The camera can reduce the harm done by underexposure by increasing the analog amplification before A->D conversion, by multiplying the numbers in the digital data by some factor, or by applying heavier noise reduction. For JPGs, often all three are used.

 

[D Cox]

That's a problem with the way the tools are designed rather than the operation itself. It's something you really want to do at the processing, rather than the post-processing stage, and some raw processors will do it automatically.

I'm sure I've said it before, but what I'd really like is an option for the camera to record a jpeg (if you shoot raw+jpeg ... or the imbedded preview) at the set (or calculated in Auto mode) ISO and the RAW file at base ISO with the intended ISO saved as a setting with a flag telling the software to "apply" that ISO.

- Dennis
--
Gallery at http://kingofthebeasts.smugmug.com

While this is not completely unreasonable, some cameras will actually add less noise to an image at higher ISO settings.

By increasing the amount of noise reduction in the JPG engine. Some cameras even apply noise reduction to "raw" files.

In a few cases, increasing the gain of the analog amplifier stage may reduce noise.

Thus in a low light situation you may very well get a little less noise shooting at ISO 3200, then at ISO 100 and lightening up 5 stops when you process the RAW file.

If you are not familiar with the specifics of your camera, the safe low-light move is to maximize exposure as much as feasible, then use the highest ISO that doesn't blow out important highlights.