From DXOMark: More pixels offsets noise3

Started May 30, 2009 | Discussions thread
ejmartin Veteran Member • Posts: 6,274
Re: From DXOMark: More pixels offsets noise3

plevyadophy wrote:

From a practical perspective it struck me as "hocus pocus mumbo
jumbo". I mean really (!), who on earth buys a high res camera so
that they can print at lower resolution/smaller print sizes so as to,
as they call it, "normalize" the noise/data/image. Really?!!!!
[raised eyebrow]

What DxO realizes, and most photographers do not, is that noise is scale dependent -- it varies with spatial frequency in the image. That means that higher resolution automatically brings with it higher noise at the pixel level (the Nyquist frequency), even if noise is the same at a given fixed spatial frequency. I showed this some time ago with the example of the 40D and 50D:

http://forums.dpreview.com/forums/read.asp?forum=1000&message=31708796

If your nerd side is interested in the underlying cause of the rise in noise with smaller photosites, see

http://forums.dpreview.com/forums/read.asp?forum=1019&message=31922352
http://forums.dpreview.com/forums/read.asp?forum=1019&message=31922793

That may all sound good to those wishing to justify buying a high
pixel cam, but real life often throws these kinda lab tests out of
the window. For example, I have seen comparison shots taken of the
indentical scene with a Sony a900 (24.6Mpix) -v- Nikon D3 (12Mpix);
the Sony had sharper defined fine detail, however in deap shadow
areas the Nikon CLEARLY outresolved the Sony for one simple reason
............... there was no noise obliterating detail. I am sure the
Sony image could be downsampled (and normalised [yawn]) and look much
cleaner, but the detail would be lost forever.

Are we talking camera jpegs? RAW? At what ISO? Were the images taken under identical conditions? There are lots of variables here, so how are you isolating pixel size as the single cause of the difference you are seeing?

I think you'll also find the differences to be a lot less if the D3x is substituted for the A900; same sensor, but Nikon seems to get more out of it.

I have also seen the Canon marketing hype at work i.e. putting
ISO256K on a camera that clearly shouldn't have that high an ISO. The
result? Whilst it performed well in lab tests, when used for what
most people would use high ISO for (namely taking low light shots,
and in the case of the test under incandescant light) it was
outgunned SIGNIFICANTLY by the Nikon camera that is a true ISO256K
camera (and again, whilst downsampling, and all that "normalising"
mumbo jumbo might make the Canon look as clean as the Nikon, the fine
detail has been zapped forever by noise).

Here you are somewhat correct. One application where larger photosites have a distinct advantage is high ISO, where camera read noise is a significant factor. The 5D2 suffers at high ISO from having excessive banding noise, which is a real detriment to image quality. However, this has less to do with the small photosites than it does with noisy electronics off the sensor. Nikon does a much better job controlling this sort of pattern noise. So again, with myriad differences among camera designs, why are you so sure that image quality differences can be attributed to photosite size?

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tko
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