ISO question

[Iliah Borg]

My understanding is the ISO standard for digital camera speed applies to the mapping from exposure (light reaching the sensor) to the lightness in the resulting sRGB JPEG file.

JPEG is not mentioned in the standard. What is mentioned is sRGB and sYCC, and "signal output". It could be any format that can be converted to RGB.

Please don't turn "Don't eat from it" into "Don't eat from it and don't touch it", nothing good came of it. I hope you recognize the source.

 

[Brian Kimball]

Increasing the lightness when producing a JPEG from a RAW file changes the ISO Speed of the process.

I don't believe the digital ISO standard makes any reference to a user post processing a raw file.

I see what you're getting at--the ISO standard specifically acknowledges that digital cameras can achieve their desired output through digital processing after the image data has been captured.

But just because pushing the exposure slider in Lightroom on a raw file is like how some cameras implement changes in ISO, does not mean it is a change in ISO.

Analogy != Reality

 

[Chato]

I am not interested in shooting with film. I prefer digital.

Is that your response to film having real ISO? In other words you have no response, and Unable to admit anything, prefer to Troll.

"ISO Speed" is a way of characterizing a process.

For film, it characterizes the mapping of exposure to negative density.

For Digital, it characterizes the mapping of exposure to image lightness in the JPEG file.

The internal mechanisms of the process are not relevant.

A film can be ISO 400 when processed in a standard fashion , and ISO 800 when "push processed".

Increasing the lightness when producing a JPEG from a RAW file changes the ISO Speed of the process.

What are you referring to when you say "real ISO"?

Compare ISO 100 film pushed to the normal development of ISO 800 film. In other words the "sensor" in film is actually more sensitive to light whereas the sensor in digital is not.

 

[Brian Kimball]

Compare ISO 100 film pushed to the normal development of ISO 800 film. In other words the "sensor" in film is actually more sensitive to light whereas the sensor in digital is not.

I would recommend re-adjusting your expectations by removing the figurative concept of "sensitivity" from your literal understanding of digital camera ISO.

This is unfortunately what happens when we learn from sources speaking figuratively / analogously. It just doesn't hold up under scrutiny.

Generally speaking, 1 photon begets 1 electron on a digital camera's sensor, and it's never been any different. The ISO standard does not specify what to do with those electrons-- just how to map a scene's luminance to the lightness of the final image (usually a JPG) produced by the camera.

Thus each camera maker is challenged with finding their own way to best count these electrons and later how to multiply those counts in ways that produce the most pleasing final image (usually a JPG) at the correct lightness for that ISO.

 

[Michael Fryd]

Increasing the lightness when producing a JPEG from a RAW file changes the ISO Speed of the process.

I don't believe the digital ISO standard makes any reference to a user post processing a raw file.

I see what you're getting at--the ISO standard specifically acknowledges that digital cameras can achieve their desired output through digital processing after the image data has been captured.

But just because pushing the exposure slider in Lightroom on a raw file is like how some cameras implement changes in ISO, does not mean it is a change in ISO.

Analogy != Reality

The ISO Speed characterized how the input (light on the sensor) maps to the output (lightness in the JPEG or other RGB file).

It is not concerned with how much of the process is analog, and how much is digital.

The ISO speed doesn't apply to RAW files, as they are not JPEG (or other RGB files) that have a defined lightness.

 

[Brian Kimball]

Increasing the lightness when producing a JPEG from a RAW file changes the ISO Speed of the process.

The ISO speed doesn't apply to RAW files, as they are not JPEG (or other RGB files) that have a defined lightness.

Juxtapose the above two statements and you'll see why I responded.

"Increasing the lightness when producing a JPEG from a RAW file" is like changing the ISO, but does not actually "change the ISO Speed of the process" because, as you yourself stated, "The ISO speed doesn't apply to RAW files" and thus a user post-processing a raw file is not addressed in the ISO standard.

Other than that quibble, we're in complete agreement.

 

[Chato]

Compare ISO 100 film pushed to the normal development of ISO 800 film. In other words the "sensor" in film is actually more sensitive to light whereas the sensor in digital is not.

I would recommend re-adjusting your expectations by removing the figurative concept of "sensitivity" from your literal understanding of digital camera ISO.

This is unfortunately what happens when we learn from sources speaking figuratively / analogously. It just doesn't hold up under scrutiny.

Generally speaking, 1 photon begets 1 electron on a digital camera's sensor, and it's never been any different. The ISO standard does not specify what to do with those electrons-- just how to map a scene's luminance to the lightness of the final image (usually a JPG) produced by the camera.

Thus each camera maker is challenged with finding their own way to best count these electrons and later how to multiply those counts in ways that produce the most pleasing final image (usually a JPG) at the correct lightness for that ISO.

The scientific term "ISO" was invented for film. It represents how the chemicals composing film react to light. The digital camera sensor, no matter what the ISO is set for does not, in any way increase it's sensitivity to light. Yet I suspect that most camera users do indeed thing that the sensor sensitivity is altered when the user raises the ISO.

 

[Brian Kimball]

Compare ISO 100 film pushed to the normal development of ISO 800 film. In other words the "sensor" in film is actually more sensitive to light whereas the sensor in digital is not.

I would recommend re-adjusting your expectations by removing the figurative concept of "sensitivity" from your literal understanding of digital camera ISO.

This is unfortunately what happens when we learn from sources speaking figuratively / analogously. It just doesn't hold up under scrutiny.

Generally speaking, 1 photon begets 1 electron on a digital camera's sensor, and it's never been any different. The ISO standard does not specify what to do with those electrons-- just how to map a scene's luminance to the lightness of the final image (usually a JPG) produced by the camera.

Thus each camera maker is challenged with finding their own way to best count these electrons and later how to multiply those counts in ways that produce the most pleasing final image (usually a JPG) at the correct lightness for that ISO.

The scientific term "ISO" was invented for film.

No and no. It's not a scientific term and it wasn't invented for film.

ISO stands for International Standards Organization and by itself has nothing to do with photography or film--they are a general purpose standards body. Talking about film speed in terms of "ISO" is just a short-hand way of specifying how a film's speed relates to the ISO's published standard. Hint: their film standards are based on an older standard, commonly called ASA, and even THAT is a misnomer- the acronym ASA actually stands for American Standards Association, now renamed to American National Standards Institute, an organization that is ALSO a general purpose standards organization, not a photography organization.

It represents how the chemicals composing film react to light. The digital camera sensor, no matter what the ISO is set for does not, in any way increase it's sensitivity to light. Yet I suspect that most camera users do indeed thing that the sensor sensitivity is altered when the user raises the ISO.

Digital camera sensors do not follow any of the three ISO film standards that I linked to in this post.

Digital camera sensors follow ISO's digital camera standard, titled "Photography — Digital still cameras — Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index", which has nothing to do with film and in no way requires the sensor to change its "sensitivity."

Thus, the whole point of this subthread, the statement "ISO is a lie", which you defended, is based on silly confusions and misunderstandings.

 

[bobn2]

Compare ISO 100 film pushed to the normal development of ISO 800 film. In other words the "sensor" in film is actually more sensitive to light whereas the sensor in digital is not.

I would recommend re-adjusting your expectations by removing the figurative concept of "sensitivity" from your literal understanding of digital camera ISO.

This is unfortunately what happens when we learn from sources speaking figuratively / analogously. It just doesn't hold up under scrutiny.

Generally speaking, 1 photon begets 1 electron on a digital camera's sensor, and it's never been any different. The ISO standard does not specify what to do with those electrons-- just how to map a scene's luminance to the lightness of the final image (usually a JPG) produced by the camera.

Thus each camera maker is challenged with finding their own way to best count these electrons and later how to multiply those counts in ways that produce the most pleasing final image (usually a JPG) at the correct lightness for that ISO.

The scientific term "ISO" was invented for film. It represents how the chemicals composing film react to light. The digital camera sensor, no matter what the ISO is set for does not, in any way increase it's sensitivity to light. Yet I suspect that most camera users do indeed thing that the sensor sensitivity is altered when the user raises the ISO.

Whilst someone here will castigate me for using Wikipedia, it's a decent source to understand the history of photographic 'speeds' and exposure indices.

Film speed - Wikipedia

en.wikipedia.org

'ISO' is just the latest term for such an index. As the article shows, there were all sorts of them, before the standards bodies got involved. ISO is the 900lb gorilla amongst standards bodies, and inherited all the previous ones.

So, before talking about 'ISO', it's a good idea to work out what is an exposure index. The mistake that is often made is that it is related to some intrinsic physical property of the sensitive medium, be it film or silicon. It isn't, it's just a guide to aid setting exposure using that film or media. The standards evolved to provide some consistency, in negative film by definition of a 'speed point' in the density characteristic of the film, that provided a reference. For digital, what has been defined is a 'lightness point'. That's all. There is nothing which says anything about chemical processes, electronic processes, pixel responsivity, grain size or so on. In the case of film, the process needs to be defined with the exposure index, since it does affect the index. In the digital standard not even that.

The problem many people seem to have is that ISO has been explained to them as a physical process, that it's very hard to think of it in any other terms. That explanation is wrong, I'm afraid.

 

[robert1955]

Compare ISO 100 film pushed to the normal development of ISO 800 film. In other words the "sensor" in film is actually more sensitive to light whereas the sensor in digital is not.

I would recommend re-adjusting your expectations by removing the figurative concept of "sensitivity" from your literal understanding of digital camera ISO.

This is unfortunately what happens when we learn from sources speaking figuratively / analogously. It just doesn't hold up under scrutiny.

Generally speaking, 1 photon begets 1 electron on a digital camera's sensor, and it's never been any different. The ISO standard does not specify what to do with those electrons-- just how to map a scene's luminance to the lightness of the final image (usually a JPG) produced by the camera.

Thus each camera maker is challenged with finding their own way to best count these electrons and later how to multiply those counts in ways that produce the most pleasing final image (usually a JPG) at the correct lightness for that ISO.

The scientific term "ISO" was invented for film.

I would not call it a scientific term. Nor is it a unit in the metric system.
It is only a reference to an industry standard, or rather several standards in a couple of iterations of film and a different one again in several iterations for digital. One thing they have in common is that they are output oriented, so what you are saying next is not correct:

It represents how the chemicals composing film react to light. The digital camera sensor, no matter what the ISO is set for does not, in any way increase it's sensitivity to light.

I think for a 2019-going-on-2020 discussion, it is wiser to forget about film ISO. Many here do not know enough about it or misunderstand what they think they now. IMO it really does not help in understanding what can happen when you turn that ISO-dial

Yet I suspect that most camera users do indeed thing that the sensor sensitivity is altered when the user raises the ISO.

It is unfortunately what they hear far too often.