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How is the native ISO of a digital camera determined ?
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AuthorTopic: How is the native ISO of a digital camera determined ? Read 34959 Times
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How is the native ISO of a digital camera determined ?on: September 7, 2020 at 4:04 pm
Andrew,
Can you please explain how you shot the two images that show less noise at a lower ISO?
If the photos were not lightened or darkened in post, then the higher-ISO image necessarily had a lower exposure, hence a <span style=”text-decoration: underline;”>lower</span> S/N ratio. Therefore, I assume you treated them differently in post.
If one was lightened in post, then it seems to me that you are venturing into the question of ISO invariance–hence, whether there is more degradation by lightening in post or by raising ISO.
Dan
Re: How is the native ISO of a digital camera determined ?Reply #1 on: September 7, 2020 at 4:07 pmThe only difference in the two when shot is the setting of ISO. The exposure is the same. And of course the normalization of the brightness of the raw in LR.
Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)”
Re: How is the native ISO of a digital camera determined ?Reply #2 on: September 7, 2020 at 7:50 pm<span style=”color: #000000; font-family: barlow, sans-serif;”>The only difference in the two when shot is the setting of ISO. The exposure is the same. And of course the normalization of the brightness of the raw in LR.</span>
Exactly my point. That’s not a minimal contrast: you weren’t looking at the effect of ISO alone, but rather comparing in-camera and in-post amplification. “Normalization of brightness” means that you brightened the low ISO photo in LR to make it as bright as the photo taken with the higher ISO. That tells us is that the camera you used isn’t ISO invariant: you got more degradation amplifying in post than in camera. It doesn’t tell us what happens when people increase ISO to offset a lower exposure, mistakenly thinking that it is equivalent to increasing exposure.
If you take two shots that have the same brightness before post, one with a low ISO and a second with a high ISO and a shorter exposure to compensate–what people do when they think ISO is part of an “exposure triangle”–the shot with a higher ISO will always have more noise. The noise floor isn’t changed, but the amount of signal is reduced by the lower exposure, giving you a lower S/N ratio. That appears as greater noise when you amplify the signal by raising ISO because that amplifies noise as well as signal.
That’s what people mean when they say that increasing ISO increases apparent noise.
Re: How is the native ISO of a digital camera determined ?Reply #3 on: September 7, 2020 at 7:56 pmYou are my missing the point.
The exposure is identical. The ISO is not.
The higher ISO has LESS noise.
The lower ISO was not edited. The higher ISO was normalized. With this kind of camera.
Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)”
- This reply was modified 3 years, 7 months ago by Andrew Rodney.
- This reply was modified 3 years, 7 months ago by Andrew Rodney.
Re: How is the native ISO of a digital camera determined ?Reply #4 on: September 8, 2020 at 8:26 amNo, I didn’t miss the point. Your posts conflate two different issues, and it’s important to clarify the distinction.
1. When people mistakenly think that ISO is part of an exposure triangle, they are thinking about settings that will produce <span style=”text-decoration: underline;”>the same</span> distribution of luminance values in the captured image. They trade off increased ISO for decreased shutter speed or a narrower aperture. This was what you were discussing in post #6. For that situation, the answer is that increasing ISO while decreasing exposure by a comparable amount to maintain a given luminosity in the capture, will generate more noise in the final image.
2. Your photos address an entirely different question: If you underexpose and then increase luminosity in the final image in one of two ways, increasing ISO or increasing luminosity in post, which creates more noise? In that case, the answer depends on both the camera used and the ISO range in question. But for many cameras, including mine, if the ISO range is fairly low, amplifying in camera (increased ISO) creates less noise than increasing brightness in post. That’s what your photos show. If I’m not mistaken, the claim for “ISO invariant” sensors is that this is for all practical purposes not true for them, and even for ISO-non-invariant cameras, my vague recollection of the relevant charts is that once one gets to a high enough ISO, there isn’t a practical difference.
Re: How is the native ISO of a digital camera determined ?Reply #5 on: September 8, 2020 at 8:34 amsorry–I don’t know why the website translated an underlined “the same” into the almost unreadable ” <span style=”text-decoration: underline;”>the same</span>”
Re: How is the native ISO of a digital camera determined ?Reply #6 on: September 8, 2020 at 8:53 amYou missed my point indeed; increase ISO doesn’t necessary increase noise. And it didn’t. That was my point.
I didn’t go into details as to why this was the case with this kind of camera; you did. I don’t disagree expect no, this had nothing to do with the ISO 100 image being altered (it wasn’t).
The Exposure triangle is bogus. The concept of a misunderstanding by many that “Higher ISO always causes more noise” is equally bogus.
We can further go into detail as to why the concept is bogus for others but they should accept; “Higher ISO can cause less noise” because it’s been shown to be true.
Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com)”
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