D600 High ISO in DX

Started Nov 23, 2012 | Questions thread
bobn2
bobn2 Forum Pro • Posts: 62,042
Re: Roger's optimum pixel pitch of 5um
1

Leo360 wrote:

bobn2 wrote:

Leo360 wrote:

The resolution of a digital image depends (among other things) on your sampling rate (Nyquist theorem) and pixel size has A LOT to do with it.

Yes, but you were talking of the resolution of a pixel. There is no 'resolution' at a pixel level, only when you look at areas containing many pixels.

I think you misunderstood what I said. Resolution of a single sample makes no sense and I never talked that way.

You talked thusly:

'This is why pixel peeping reveals more noise-per-pixel for smaller photosites. The price to pay is reduced resolution.'

´╗┐So, to evaluate noise you are looking 'per pixel'. Now, when you talk about 'resolution' you are no longer talking 'per pixel', or are you? You can't include 'per pixel' in the one and not be talking 'per pixel' with respect to the other. (apart from, of course, as we learn below, there is  no noise 'per pixel').

For a fair comparison we have to establish a common bandwidth, i.e. common sampling rate.

Not 'i.e. common sampling rate'. You don't have to resample to observe over a common bandwidth, you just observe the same size, or normalise to the same bandwidth. It is about bandwidth, not resampling.

Hence, resampling. For the sake of argument let this common rate be the sampling rate of the lower-res camera (D600 in DX). I resample D3200 image down to match it.

Correct me if I am wrong, but I think that you will have to jump through several hoops to match 4x4 um pixel SNR to 6x6 um one.

You cannot measure SNR in a single pixel in a single photograph. Now think on the implications of that.

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Bob

Did I say anything about a single photograph? To measure pixel readings statistics one shoots repeatedly in controlled environments with constant light, exposure, etc. You get mean, variance, probability distribution etc in due course of statistical analysis.

This now becomes throughly artificial, that you make the multiple observations of the same pixel over multiple exposures. It is not even guaranteed that the noise so observed would match the noise observed in the spatial domain. A thoroughly artificial result of no interest.

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Bob

Bob, you brought it "single pixel in a single photograph", not me.

You brought it up. You talked about matching a 4x4 micron pixel to a 6 by 6 one. You are comparing the SNR in a singular pixel with another one and that makes no sense. When I point that out you propose that you shoot repeatedly, observe the same pixel over repeated observations. All that makes sense is comparing noise over equal areas of equal sized output images, not comparing a 4x4 pixel with a 6x6 one. Making multiple observations over time has nothing to do with it.

I just replied with the text-book definition of how one samples stochastic processes

Without understanding. Most textbooks are talking about variation in the temporal dimension, since they are talking about time varying signals. In photography we have a spatially varying signal, and you didn't spot that you just need to swap space for time.

Anyway, Roger claims that 5um is the optimum pixel pitch for a CMOS sensor. Should one take it seriously? If yes, then we have a winer -- D800 .

I don't take nonsense seriously, even if by chance it gives a sensible result. The reason the D800 is the tops is because it has the smallest pixels of an FF camera, not because they happen to be 5 micron.

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Bob

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