Shooting high ISO vs underexposing and lifting in post question

Started 3 months ago | Discussions thread
Slaginfected Contributing Member • Posts: 745
Re: "Magic handwaving" or simple physics

J A C S wrote:

Slaginfected wrote:

Because I'm evil, here something for you: People wrote back in the days that the D750 is better suited for low-light images than the D810. And it seems like it doesn't stop there, you see similar things being mentioned between Z6 and Z7 (and between their 2nd iteration version), between A7III and A7rIII (and also between A7rIII and A7rIV, meaning there must be a larger difference between A7III and A7rIV) etc. So ... any explanations for that?

People write that Earth is flat, that Elvis is still alive, and that the man in the sky is watching us, just to mention a few more...

You know, the problem here at DPR is, that quite a few people can explain you all the nitty gritty details of how a sensor works and the RAW data and a couple other things. But noone can give you even an estimate of how the SNR of the data changes / is affected by the processing of the data afterwards, numerical problems on the way, calculation error estimations etc.

You are evil, indeed. And wrong. The SNR of the data does not change with processing. It is data, it should be in a "lockbox", and what you are talking about is noise in the processed image. How noise changes under linear transformations (think about the color matrix) is known, and I have hinted in this before. DXO even plot noise ellipses.

You mean these fancy things which are much larger with higher res cameras than with lower res cameras towards higher ISOs and less available light? And if we stray from daylight type light it gets even worse?

I do not want to go there because you would dismiss it anyway regardless of the fact that you asked for it. One can explain what happens under some kinds of non-linear processing, as well but that would be too technical.

Numerical problems are rarely problems but sometimes they can create posterization; we had threads like this before.

Calculation error estimates are a topic of numerical analysis, but it would be too much for our purposes. There is so much noise in our images that we do not need to worry about that.

So you are completely wrong about your claim in bold above.

Because if someone were able, they would have thrown this around already, including my way. Which didn't happen so far, which you could count as a strong indication nothing like this exists. Still, that doesn't prevent people from telling me that the stuff I'm seeing when actually processing files is wrong etc. Seriously?

Yes. All the theory in the world means nothing if we are not seeing what you think you are.

Plus there are quite a few questions surrounding that topic. If the results would be all the same, why do camera makers give cameras different max ISO ratings? For example, the A7 line seems to have rather consistent max ISO ratings, and they have a certain difference between them, which seems to match up, roughly, the processing latitude differences you see at higher ISOs, for example. Strange, isn't it? And there are many more such questions combined with logical reasoning which just gives strong indication that "there is something".

Many cameras today and my Canons in the past had completely useless scaled high ISO because it made them looked better.

And while I'm throwing around questions: How much experience do you have with low-light photography? You know, short exposure times, not really ideal light, maybe even LED lights thrown into the mix, stuff like that? Higher 4 and lower 5 digit ISOs. Just wondering ...

None of use ever shoots in low light, I guess...

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