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Increasing the ISO is a contributory cause of increased noise

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In my opinion the confusion stems from ambiguity about which metering system is being used and which metering mode. No one ever specifies which they're using.

If you use a handheld incident meter you can adjust your shutter speed and aperture independent of ISO in a way that you know will reduce noise—placing your shadows, midtones, and highlights to get the best performance out of the sensor for the particular scene.

If you use the in-camera meter you're stuck in an endless loop of uncertainty because when you change one parameter, the camera's "invisible" adjustments are making their mischief under the hood.

For my normal shooting the scene dynamic range makes the biggest difference. If I'm shooting a moody portrait of a pale-skinned North Dakotan but I want lots of shadow detail I'm going to have more trouble with noise because I can't capture the skin tone detail without the danger of crushing my blacks. Trying to bring up the shadows risks evoking noise.

Situational is the short answer.
 
Tom Axford said:
Bill Ferris said:
Unfortunately, many novice photograhers and even a fair number of experienced photograhers, believe a change to ISO directly affects exposure. It's a misunderstanding that limits a person's ability to get the most from their camera and their photo processing & editing app of choice.
Click to expand...
I agree, but I think that belief may be the result of poor teaching in the first place. Any suggestion that changing ISO directly affects exposure is wrong. Just as it is wrong to suggest that changing ISO directly affects noise.

However, I think it is perfectly ok to tell beginners that, as a general rule, photos taken at high ISO have less exposure and more noise than photos taken at low ISO. It is sensible to add that there are exceptions to the rule, but the rule is true for the great majority of photographs.

It is equally sensible to tell beginners, who have just started to experiment with the ISO setting on their cameras, that, as a general rule, setting a high ISO will lead to poorer image quality than setting a low ISO. Again, point out that there are exceptions, but they are rare.
Click to expand...
If the ISO has been raised in order to use a faster shutter speed, the image quality should be better, not worse. An image which is blurred by camera (or subject) movement not only looks bad because it's blurry, it also has a lower S/N ration. (The higher spatial frequency signal is reduced.)

Don
 
Tom Axford said:
When teaching students, my experience has been that students are not like computers; they do not hang on every word I say and interpret each word exactly and precisely like a computer processes a computer program.

With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture, I think it would be perfectly ok to say something like:

"As a general rule, whenever you increase the ISO, there is a penalty to pay in reduced image quality [then show some examples of low ISO and high ISO images and maybe introduce the term "noise"]. As with all good rules, however, there are some exceptions. These exceptions are rare and we will ignore them for the time being."
Click to expand...
You would be lying to them. It would be hard to make them unlearn something wrong later - it would be easier to tell them the truth at the beginning. You raise the ISO to improve the IQ, this is the whole point of our cameras having hardware ISO. You are forced to do it by the conditions, and your desire to get the best IQ in those conditions. If you do not do it, with the presumption that your shoot in some automatic mode, you would get too thin DOF and/or motion blur which ruins the IQ.
Tom Axford said:
I think it is guaranteed that you will be labelled as a boring teacher if you try to explain all the exceptions whenever you introduce a new rule. And students learn less from boring teachers and that is often why they misapply the rules.
Click to expand...
I have a friend who was my mentor as a young faculty. She told me once that the best way to get great evaluations was to lie to the students. She never did it though.
 
FingerPainter said:
... a response that seems somewhat of a non-sequitur from the post of yours to which I responded, and to the OP. In those you talked about the meaning of the word "causes", philosophers of causality, and a discussion about when it is ok to say that A causes B, about the language we use.

I tried to meet you at your own level and address the question which you purported to want input on. I gave you a response that dealt specifically with the semantic issues you raised. You have chosen not to directly address anything I said. You don't seem to have liked where that discussion was headed. Instead, you seem to have shifted from semantics to effective teaching. Without saying so in so many words, your response seems to amount to "saying 'A causes B under condition 1 and causes (not B), otherwise' is too complex for students to grasp, so we should tell them 'Generally A causes B. There are a few rare exceptions that we'll deal with later.'"

So you want to shift the field of discussion from semantics to effective pedagogy. OK, I'll accommodate you again. Your approach is setting student up for failure at the point where they encounter those exceptions. By then, the students have entrenched a fundamentally wrong conceptual model. To make sense of the exceptions, the successful student will have to throw out the model you have been building to that point and replace it with a different one. That is an inefficient way to teach, and prone to greater failure.

When B is "greater image noisiness", the correct general statement of causation is "C causes B", where C is "decreased exposure". No need to resort to "contributory causes". No need to deal with exceptions which you will relegate to dealing with at some unspecified time. Dealing with exceptions later destabilizes conceptual models. "C causes B" has more simplicity and is therefor easier for students to grasp than your proposal. And it has no exceptions, so there is no need for a later radical adjustment to the conceptual model.
FingerPainter said:
When teaching students,
Click to expand...
Do you actually have formal training in pedagogy? What you have written here doesn't sound to me like you do.

For ten years I held a position in which I was responsible for the quality of education received by tens of thousands of students. You can be sure that during that time I had more professional upgrading in pedagogical method than did the average teacher. I consulted with leading national experts from several different countries. I wasn't limited to instruction received at just one average teacher's college.

Ysarex and bobn2 both taught at the post-secondary level, and both seem convinced of the importance of emphasizing the relationship between noise and exposure. Both have also talked about the damage done when students have to adjust their conceptual model from an early-formed incorrect model to a different model later on.
Click to expand...
Well, I also taught photography at college level, but that was in the film era. If teaching it today, I would also start with the concept of shot noise and exposure.
FingerPainter said:
FingerPainter said:
my experience has been that students are not like computers; they do not hang on every word I say and interpret each word exactly and precisely like a computer processes a computer program.
Click to expand...
Some will, some won't. All will start to build a conceptual model as they take in whatever words they do pay attention to.
FingerPainter said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
Life would be simple if the ISO was just a lightness control. The problem is that it changes several different things at once. And the changes don't happen at every step of the scale. And the manufacturers don't document what happens.
FingerPainter said:
FingerPainter said:
I think it would be perfectly ok to say something like:

"As a general rule, whenever you increase the ISO, there is a penalty to pay in reduced image quality [then show some examples of low ISO and high ISO images and maybe introduce the term "noise"]. As with all good rules, however, there are some exceptions. These exceptions are rare and we will ignore them for the time being."
Click to expand...
And I think that's a lousy way to instruct beginners because it implants at the beginning of the formation of their internal conceptual models that the primary association of noise is with ISO, rather than that noise is primarily and causally associated with exposure. The time to introduce "noise" is when you are explaining exposure, not when you are explaining ISO.
Click to expand...
Yes. Or better, when you introduce light.
FingerPainter said:
That's because it is exposure that is the primary factor affecting the noisiness of an image. This also means you don't have to deal later with the rare exceptions that overturn your general layout of the conceptual model because, unlike the non-causal relationship of ISO to noisiness, there are no exceptions to the causal relationship between exposure and noisiness.
FingerPainter said:
I think it is guaranteed that you will be labelled as a boring teacher if you try to explain all the exceptions whenever you introduce a new rule.
Click to expand...
So the choice is to either leave the exceptions to later while initially forming an incorrect conceptual model, or to teach something where there actually are no exceptions.
FingerPainter said:
And students learn less from boring teachers and that is often why they misapply the rules.
Click to expand...
The problem is, in your approach, you haven't actually taught them the rule. Instead of a rule incorporating direct causation, you have taught them a non-causal correlation that only holds under specific conditions, and you have failed to describe what happens when those conditions do not apply. That's not a rule.
Click to expand...
 
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57even said:
J A C S said:
57even said:
Tom Axford said:
There is an argument raging in another thread (in the Beginners Questions forum!) about whether or not increasing the ISO causes noise to increase.

As I see it, the disagreement essentially revolves around the meaning of the word "causes".

Some people appear to think that a cause must be a sufficient cause for it to called a cause. Others (including me) think that a contributory cause may also be called a cause.

Philosophers of causality distinguish between necessary causes, sufficient causes and contributory (or partial) causes. A contributory cause is neither necessary nor sufficient. It is sufficient only if other conditions hold as well.

Increasing the ISO is a contributory cause of increased noise because if various other conditions hold (such as the camera being in an auto-exposure mode), then increasing the ISO causes a decrease in exposure which in turn causes fewer photons to be collected by the sensor, which in turn causes an increase in the noise (relative to the signal).

What is your opinion on this matter?
Click to expand...
Actually, it causes noise to decrease. It indirectly causes the ratio of noise to signal to increase (or SNR to decrease).

Even this is only true under the condition that image lightness is maintained and integration time is not long enough to create dark noise.
Click to expand...
Actually, in this case, the (standard deviation of the) noise increases with the ISO, assuming that the higher ISO forces us to lower the exposure.
Click to expand...
The standard deviation of the input noise (other than read noise) decreases as exposure decreases. Shot noise = sqrt(signal), PRNU = k*signal.

The standard deviation of output pixels only increases when lightness is equalised because SNR is lower, but it also depends on processing and other factors that have nothing to do with ISO, like resizing.

Nor does ISO correlate directly to an increase in output referred noise unless the ISO amplifier is being used to add voltage gain to the signal and the ADC is clipping that signal, which is not always the case. In many cases, the lightness adjustment is applied later during digital processing.
Click to expand...
Please read the phrase I underlined.
 
J A C S said:
57even said:
J A C S said:
57even said:
Tom Axford said:
There is an argument raging in another thread (in the Beginners Questions forum!) about whether or not increasing the ISO causes noise to increase.

As I see it, the disagreement essentially revolves around the meaning of the word "causes".

Some people appear to think that a cause must be a sufficient cause for it to called a cause. Others (including me) think that a contributory cause may also be called a cause.

Philosophers of causality distinguish between necessary causes, sufficient causes and contributory (or partial) causes. A contributory cause is neither necessary nor sufficient. It is sufficient only if other conditions hold as well.

Increasing the ISO is a contributory cause of increased noise because if various other conditions hold (such as the camera being in an auto-exposure mode), then increasing the ISO causes a decrease in exposure which in turn causes fewer photons to be collected by the sensor, which in turn causes an increase in the noise (relative to the signal).

What is your opinion on this matter?
Click to expand...
Actually, it causes noise to decrease. It indirectly causes the ratio of noise to signal to increase (or SNR to decrease).

Even this is only true under the condition that image lightness is maintained and integration time is not long enough to create dark noise.
Click to expand...
Actually, in this case, the (standard deviation of the) noise increases with the ISO, assuming that the higher ISO forces us to lower the exposure.
Click to expand...
The standard deviation of the input noise (other than read noise) decreases as exposure decreases. Shot noise = sqrt(signal), PRNU = k*signal.

The standard deviation of output pixels only increases when lightness is equalised because SNR is lower, but it also depends on processing and other factors that have nothing to do with ISO, like resizing.

Nor does ISO correlate directly to an increase in output referred noise unless the ISO amplifier is being used to add voltage gain to the signal and the ADC is clipping that signal, which is not always the case. In many cases, the lightness adjustment is applied later during digital processing.
Click to expand...
Please read the phrase I underlined.
Click to expand...
I wrote it. What don't you understand?
 
Tom Axford said:
There is an argument raging in another thread (in the Beginners Questions forum!) about whether or not increasing the ISO causes noise to increase.

As I see it, the disagreement essentially revolves around the meaning of the word "causes".

Some people appear to think that a cause must be a sufficient cause for it to called a cause. Others (including me) think that a contributory cause may also be called a cause.

Philosophers of causality distinguish between necessary causes, sufficient causes and contributory (or partial) causes. A contributory cause is neither necessary nor sufficient. It is sufficient only if other conditions hold as well.

Increasing the ISO is a contributory cause of increased noise because if various other conditions hold (such as the camera being in an auto-exposure mode), then increasing the ISO causes a decrease in exposure which in turn causes fewer photons to be collected by the sensor, which in turn causes an increase in the noise (relative to the signal).

What is your opinion on this matter?
Click to expand...
The ISO setting puts an upper limit on the exposure you can use without clipping the highlights. Thus the ISO setting affects the exposure, if set before the shutter speed and aperture. Those who prioritise the exposure settings may tell you the exposure is not affected by the ISO setting.

However, regardless of what gets set first, the ISO setting indicates the best achievable noise/cleanness. The higher the ISO, the more visible noise there is in the image.
 
FingerPainter said:
FingerPainter said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
 
Quarkcharmed said:
FingerPainter said:
Quarkcharmed said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I think the ISO standard refers only to what is commonly called "Base ISO". It refers to the camera as a black box that outputs JPG files.

So far as I know it says nothing about setting higher "ISO" numbers. Calling that setting "ISO" is a metaphor.

Am I wrong ?

Don
 
D Cox said:
Quarkcharmed said:
FingerPainter said:
D Cox said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I think the ISO standard refers only to what is commonly called "Base ISO". It refers to the camera as a black box that outputs JPG files.

So far as I know it says nothing about setting higher "ISO" numbers. Calling that setting "ISO" is a metaphor.

Am I wrong ?
Click to expand...
Why base ISO only? When you increase the ISO setting by 1 stop, you need 1 stop less exposure to get the same jpeg output.
D Cox said:
Don
Click to expand...
 
D Cox said:
D Cox said:
...
Click to expand...
If the ISO has been raised in order to use a faster shutter speed, the image quality should be better, not worse. An image which is blurred by camera (or subject) movement not only looks bad because it's blurry, it also has a lower S/N ration. (The higher spatial frequency signal is reduced.)

Don
Click to expand...
A reduction in analog signal-to-noise ratio (SNR) when the shutter is open can have a much greater affect on perceived image quality than loss of resolution due to movement blur.

Shannon information theory describes the relationship between resolution and SNR.

C = information capacity, W = resolution [1]
C = information capacity, W = resolution [1]

The logarithmic dependence of C on SNR means a reduction in W due to an ill-chosen shutter time must be significant. The increase in blur due to shutter time is less important as camera ISO increases.

Increasing camera ISO setting does not necessarily increase W due to a shorter shutter time.

Increasing camera ISO setting always decreases SNR because unless signal level is decreased, the rendered image will become excessively bright. Increasing lens aperture and, or decreasing shutter time is required to achieve an acceptable rendered image brightness. Any presumed decrease in post-signal acquisition noise due to analog gain level can not cancel the decrease in signal level.

1. W represents bandwidth in Shannon's original paper. In our case bandwidth is determined by resolution. The W term is a sum of anything that impacts rendered image MTF 50 and pixel density (MP count). Motion blur due to camera and subject motion is only one of many ways to reduce MTF 50.
_____________________
“…the mathematical rules of probability theory are not merely rules for calculating frequencies of random variables; they are also the unique consistent rules for conducting inference (i.e., plausible reasoning)”
E.T Jaynes, Probability Theory: The Logic of Science
 
Quarkcharmed said:
D Cox said:
Quarkcharmed said:
FingerPainter said:
Quarkcharmed said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I think the ISO standard refers only to what is commonly called "Base ISO". It refers to the camera as a black box that outputs JPG files.

So far as I know it says nothing about setting higher "ISO" numbers. Calling that setting "ISO" is a metaphor.

Am I wrong ?
Click to expand...
Why base ISO only? When you increase the ISO setting by 1 stop, you need 1 stop less exposure to get the same jpeg output.
Quarkcharmed said:
Don
Click to expand...
Click to expand...
Only the same lightness, as usual lunch is not free
 
Quarkcharmed said:
D Cox said:
Quarkcharmed said:
FingerPainter said:
Quarkcharmed said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I think the ISO standard refers only to what is commonly called "Base ISO". It refers to the camera as a black box that outputs JPG files.

So far as I know it says nothing about setting higher "ISO" numbers. Calling that setting "ISO" is a metaphor.

Am I wrong ?
Click to expand...
Why base ISO only? When you increase the ISO setting by 1 stop, you need 1 stop less exposure to get the same jpeg output.
Click to expand...
No doubt, but that is not what the ISO standard is about.
Quarkcharmed said:
Quarkcharmed said:
Don
Click to expand...
Click to expand...
 
D Cox said:
Quarkcharmed said:
FingerPainter said:
D Cox said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I think the ISO standard refers only to what is commonly called "Base ISO". It refers to the camera as a black box that outputs JPG files.

So far as I know it says nothing about setting higher "ISO" numbers. Calling that setting "ISO" is a metaphor.

Am I wrong ?
Click to expand...
IDK for certain since I do not own a copy of the standard, but I believe, from hearing descriptions from those who do own a copy, that it describes the relationship between exposure Index and image lightness for exposure indices other than base as well.

What it doesn't contain is a specification of how a DSC will achieve the output at a higher EI than bae.
 
Last edited:
57even said:
J A C S said:
57even said:
J A C S said:
57even said:
Tom Axford said:
There is an argument raging in another thread (in the Beginners Questions forum!) about whether or not increasing the ISO causes noise to increase.

As I see it, the disagreement essentially revolves around the meaning of the word "causes".

Some people appear to think that a cause must be a sufficient cause for it to called a cause. Others (including me) think that a contributory cause may also be called a cause.

Philosophers of causality distinguish between necessary causes, sufficient causes and contributory (or partial) causes. A contributory cause is neither necessary nor sufficient. It is sufficient only if other conditions hold as well.

Increasing the ISO is a contributory cause of increased noise because if various other conditions hold (such as the camera being in an auto-exposure mode), then increasing the ISO causes a decrease in exposure which in turn causes fewer photons to be collected by the sensor, which in turn causes an increase in the noise (relative to the signal).

What is your opinion on this matter?
Click to expand...
Actually, it causes noise to decrease. It indirectly causes the ratio of noise to signal to increase (or SNR to decrease).

Even this is only true under the condition that image lightness is maintained and integration time is not long enough to create dark noise.
Click to expand...
Actually, in this case, the (standard deviation of the) noise increases with the ISO, assuming that the higher ISO forces us to lower the exposure.
Click to expand...
The standard deviation of the input noise (other than read noise) decreases as exposure decreases. Shot noise = sqrt(signal), PRNU = k*signal.

The standard deviation of output pixels only increases when lightness is equalised because SNR is lower, but it also depends on processing and other factors that have nothing to do with ISO, like resizing.

Nor does ISO correlate directly to an increase in output referred noise unless the ISO amplifier is being used to add voltage gain to the signal and the ADC is clipping that signal, which is not always the case. In many cases, the lightness adjustment is applied later during digital processing.
Click to expand...
Please read the phrase I underlined.
Click to expand...
I wrote it. What don't you understand?
Click to expand...
You contradicted yourself there. I do not want to drag this out further.
 
Quarkcharmed said:
FingerPainter said:
Quarkcharmed said:
With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I would say, fortunately.
 
J A C S said:
Quarkcharmed said:
FingerPainter said:
J A C S said:
[somebody wrote] With beginners, after telling them the way they can use ISO to change how they choose shutter speed and aperture,
Click to expand...
I think that is a backwards way to look at ISO that is just perpetuating a film-centric approach to understanding camera-controls. ISO is not a noise control or an exposure control. It is a lightness control, and it's use ought to be taught in that context.
Click to expand...
By ISO standard, yes, it's lightness control. Unfortunately in most modern cameras the ISO setting does much more than a mere lightness control.
Click to expand...
I would say, fortunately.
Click to expand...
Fortunately, in my DSLR, the ISO setting does absolutely nothing to the raw image data; said setting is sent in meta-data to the converter where the image noise is dutifully amplified pro rata.

--
what you get is not what you see ...
 
Last edited:
The Ghost of Caravaggio said:
D Cox said:
The Ghost of Caravaggio said:
...
Click to expand...
If the ISO has been raised in order to use a faster shutter speed, the image quality should be better, not worse. An image which is blurred by camera (or subject) movement not only looks bad because it's blurry, it also has a lower S/N ration. (The higher spatial frequency signal is reduced.)

Don
Click to expand...
A reduction in analog signal-to-noise ratio (SNR) when the shutter is open can have a much greater affect on perceived image quality than loss of resolution due to movement blur.
Click to expand...
Hello,

I do not understand your point but I certainly missed something.

It is much better to use a faster shutter speed at the cost of an image is a bit noisier when there is camera shake for instance. The final resolution decreases extremely rapidely if you use a too slow shutter speed. If this is too slow, each time you make it twice slower the resolution may decrease 4 times (2 times on each direction). This is a simplified model but in practice, I try to take a margin to avoid taking any risk.

Can you explain your point ? Just curious.
 
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