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ISO is not fake and here is the standards document
- Thread starter ElhanDobriv
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john Clinch
Senior Member
My sister and her husband were one of the first people I knew with a digital camera
I remember asking them what asa it used (I think I said asa not ISO)
i was so impressed when they said 100. I really had no idea what it would. I had was worried that they were going to say 10 or something crazy low
I’m not sure calling it gain would change very much. Would you go with the same numbers or a new system? Would we set a base which would be say iso 100 and call that say zero. Then iso 400 is 2 and iso 50 -1?
ISO in digital cameras is not the same as gain, though. Simply put, ISO defines the relation between the exposure level and the brightness of the final output image (JPEG). This can be controlled by varying the gain, but it's also possible for a camera to control ISO, not by varying the gain, but by applying the same gain regardless of ISO setting, and then adjusting the brightness of the final images instead. Gain is a method for controlling ISO, but it's not an inherently necessary one.
for a good introduction to digital ISO: https://m.dpreview.com/articles/9698391814/the-ins-and-outs-of-iso-what-is-iso
Mark S Abeln
Forum Pro
ISO is just the international standards body that promulgates a large number of technical standards in many industries.
“Exposure index” is a better technical term.
ISO isn't fake, it's a mathematical fiction - without it we wouldn't have an exposure triangle, just an exposure... duangle? which is quite lame.
tbcass
Forum Pro
I don't think fake is the right word. The standard originated in the film days and is much less relevant for digital, especially for RAW images.
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Tom
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tbcass
Forum Pro
Even that may not be relevant since most modern ISOless sensors either apply only single gain or are dual gain so most of the adjustment is applied in the JPEG processing or not at all for RAW.
Mark S Abeln
Forum Pro
I've read the standard, and I think what gets folks upset is the idea that ISO is arbitrary—which it is—but that also means that ISO is meaningless, which it is not.
Let's consider film, which is well known to have fixed ISO, but you can in fact expose the film to any ISO that you desire. I shoot Kodak Tri-X, which is ISO 400. Nowadays, I find that I get better results when I expose the film to ISO 200, getting lots of nice shadow detail. But back in the old days, I would expose it to ISO 1600, to get as much speed as possible. So in this sense, the ISO is arbitrary, and I can set it to whatever I want it to be. Yesterday I imagined that Tri-X ought to be ISO 275, today I feel that Tri-X should be 320, and tomorrow I might think that it is 500. It is arbitrary.
But arbitrary does not equal meaningless. A specific film stock is being exposed by a definite amount of light with real consequences for the resulting negative. There are consequences to exposing Tri-X at ISO 200 and there are different consequences when exposing it at ISO 1600. Likewise, there are real consequences to changing ISO in a digital camera.
But there is another side to ISO which folks sometimes don't think about, and that is how processing *must* change with a change of ISO. Changing the ISO of a film needs a change in development time, otherwise you might end up with an unusable negative. Likewise, with digital, a change of ISO of the sensor requires a change of processing; for example, boosting ISO from 100 to 200 requires boosting the electronic amplification or data scaling by 1 stop.
You could very well change the processing without changing the exposure, but again that will have real consequences: I can shoot Tri-X at 200 but develop it to 400, and I'll get different results than if I shot it at 200 and developed it at 200, or shot it at 400 and developed it at 400. In some ways this is like using the exposure compensation feature on a digital camera: you can set the camera to ISO 100 and use zero exposure compensation, and you'll get different results than if you set the camera to ISO 200 and used one stop positive exposure compensation: the exposure is the same but the results are different.
So any full change of ISO requires both a change in exposure as well as a definite change in processing, and these taken together are not arbitrary.
Exposure is typically measured in units of lux-seconds, where a lux is one lumen per square meter, and I hope that most people who've purchased a lot of light bulbs are at least somewhat familiar with lumen values. The "seconds" part of exposure is the shutter speed.
I use the term "ISO" loosely, as do most photographers, but a more general term to use is exposure index, and here is how Exposure Index is defined in digital photography:
Exposure Index = 10 lux-seconds / Exposure to reach an sRGB value of (118, 118, 118) for a neutral patch.
Please note that this takes into account both the amount of light falling on the sensor, and the processing needed to get a final result. This relationship is what gives ISO its meaning. It tells you how much exposure is needed to get a certain mid tone lightness: an ISO 100 sensor requires 0.1 lux-seconds to achieve middle gray, and an ISO 200 sensor requires half that amount. Sure, there are plenty of ways to do this, but this relationship is what remains constant.
Sure, you can arbitrarily say that ISO is defined by so many stops below sensor saturation, which used to be the standard way of doing things, but what if you want your images to have more highlight headroom? Then you arbitrarily set the ISO higher, but you'll have to change your processing to compensate, so that the above relationship still holds. After all, old digital cameras were often accused of lacking headroom. I recall one medium format camera that has an ISO of 10 according to the old sensor saturation rule, but the manufacturer arbitrarily redefined it to 100 so that they'd have far more highlight headroom—and I'm sure photographers appreciate that a lot, as the camera gives more 'malleable' files especially with respect to bright tones.
You may have two different cameras that have otherwise identical sensors, but different base ISOs; clearly, the difference will be in the processing.
What the ISO standard does include is laboratory methods for measuring exposure, specifying standard light sources, and other technical and practical matters that are important, so this isn't a 'non-standard' as many claim.
Mark S Abeln
Forum Pro
It depends on the camera and particular ISO. My Nikon D750 only applies analog gain up to about ISO 8000, with additional digital scaling beyond that, so I keep my maximum Auto-ISO at 8000, and brighten in post as needed. There are some cameras that don't have analog gain at all.
I'd argue that brightening and darkening in post is in effect changing ISO (or to be more precise, changing the Exposure Index).
tko
Forum Pro
You have any proof that you've actually read and understand that article?not if you can't afford it no. happy to claim victory by default
There's a lot of "standards" in the world. Many of them are poorly written, misunderstood, have loopholes, or are just plain cheated on. Not like the manufacturers claims are being actively checked up on by anyone or that's there's any penalty for creative interpretations.
ElhanDobriv
Leading Member
Thank you for the very detailed contribution. This explanation makes a lot of sense to me and seems to hold true to the brief explanation set out in the beginning of the document regarding the intention of an exposure index. I've tested a few cameras (JPEG output) and the required ISO for a given exposure seemed to be a constant. which would indicate to me that there's probably not too much deviation going on amongst manufacturers... although granted my sample size is small.
Yes. I use ISO 160-1000 (max) in my D90. I don't want scaling or noise reduction.
Michael Fryd
Forum Pro
I have an earlier version of that standard. In the Introduction it explains that unlike film, Digital Still Cameras have a range of exposures where they will produce good images. Therefore they don't have a speed rating, but a speed range.
The ISO standard exists in order to "harmonize" digital workflows to film workflows. The intention is that someone who is used to shooting film, can switch to digital, while still applying his film exposure methods.
The goal of this standard is not to maximize the quality of the resulting digital image, but to allow film photographers to be able to use digital cameras with minimal retraining.
So whether or not digital ISO speed ratings are "fake" is a matter of terminology. Unlike film, a single speed rating does not reflect the abilities of the underlying medium. From that perspective the speed rating is not real. However, digital speed ratings can be quite useful in predicting how dark or light a camera produced JPEG will be. From that perspective, they are real.
The ISO Speed rating is undefined for photographers who shoot raw, as the lightness of the resulting image is determined by how the raw data is processed.
To be fair, when shooting film, the ISO speed had little to do with how dark or light the final print looked. The combination of ISO speed and exposure determined how dense or thin the negative was. How dark or light the print looked was determined in the darkroom at print time, and was independent of negative density.
The ISO standard exists in order to "harmonize" digital workflows to film workflows. The intention is that someone who is used to shooting film, can switch to digital, while still applying his film exposure methods.
The goal of this standard is not to maximize the quality of the resulting digital image, but to allow film photographers to be able to use digital cameras with minimal retraining.
So whether or not digital ISO speed ratings are "fake" is a matter of terminology. Unlike film, a single speed rating does not reflect the abilities of the underlying medium. From that perspective the speed rating is not real. However, digital speed ratings can be quite useful in predicting how dark or light a camera produced JPEG will be. From that perspective, they are real.
The ISO Speed rating is undefined for photographers who shoot raw, as the lightness of the resulting image is determined by how the raw data is processed.
To be fair, when shooting film, the ISO speed had little to do with how dark or light the final print looked. The combination of ISO speed and exposure determined how dense or thin the negative was. How dark or light the print looked was determined in the darkroom at print time, and was independent of negative density.
Overrank
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In the world of conspiracy theorists believIng that “ISO is fake” is a pretty benign conspiracy
Mark S Abeln
Forum Pro
You're welcome.
Actually, the standard does require rounding of the resulting ISO values to the nearest 1/3rd stop. Similarly, focal length, f/stop, and shutter speed are also rounded to simple standard values.
But this rounding isn't too photographically significant, as it makes comparisons easier and fortunately spares us from marketing bluster. If you don't like your resulting exposure, just use a little exposure compensation.
You'll likely see greater variance between cameras because of lens transmittance and vignetting.
tony field
Forum Pro
A free standard document that encompasses the important essence of the iso standards is
CIPA DC-004
Do a Google search. I cannot provide a link from my tablet since it is a protected pdf.
https://www.google.com/search?q=cip...msung-nf-rev1&sourceid=chrome-mobile&ie=UTF-8
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Charles Darwin: "ignorance more frequently begets confidence than does knowledge."
tony
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The nearest film analogy to digital is positive slides (such as Kodachrome), not negatives. There was very little latitude for adjustment of exposure when you printed from slides.
You could push a roll of slide film to twice or even four times its nominal ISO speed by increasing the development time, but this was really for emergencies only.
There is no digital equivalent of a film negative.
Don
Michael Fryd
Forum Pro
In many ways slide film is like a camera produced JPEG. Image lightness is tied to exposure. In terms of post processing, you are limited in the magnitude of your corrections.
In many ways shooting raw is like shooting traditional negative film. Image lightness is not tied to exposure, and you have greater latitude for corrections and adjustments.
If you are shooting digital, and want to maximize quality, and your control over the process, then you should be shooting raw. Yes, it is possible to get great images with camera produced JPEGs. However, shooting JPEG adds additional constraints that are not present when shooting raw. Furthermore, there are captures that can be gotten when shooting raw, that are not practical to capture when shooting JPEG.
Now we are discussing terminology. "Equivalent" in terms of what? When you shoot raw, you can "push" (lighten) the image in post processing. Of course, the equivalence breaks down when you realize that pushing film applied to the entire roll of film. "Pushing" raw images can be done on an image by image basis. In fact, you can choose to "push" parts of the image, but not others.
So while shooting raw offers all the functionality of shooting film negatives, the reverse is not true. Film does not offer all the capabilities of digital. Whether or not that makes them "equivalent" is an issue of terminology, not functionality.
Of course, "pushing" digital is not reserved for emergencies. With most digital cameras, you can set the camera to ISO, and "push" the raw file two stops. You're going to get essentially the same result as if you had the same exposure, but the camera set to ISO 400. Again, should we avoid the "equivalence" label simply because digital offers more than film?
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