Got any links to material on that? It\'s a claim distinctly at odds with what I\'ve heard or read (and frankly, it\'s the exact same argument, just about down to those numbers, that I was reading 6 years ago, and about 4 stops of high ISO performance ago). Frankly, the only aspect that hasn\'t been changing is the conversion efficiency of the pixel well. It\'s possible that we\'re getting close to the limits of CMOS-based sensors but I\'d like to see some papers on it (feel free to link to IEEE Xplore, I\'ve got access) before I accept it.
It\'s also provably incorrect from a whole-imager perspective (even accepting it as correct regarding the silicon). Kodak\'s mixed luminance/colour filter array gives 1 to 2 stops on its own (depending on the exact pattern chosen) via changes to the CFA. That leaves 0.5 stops of your claim for actual improvement of microlenses and fill factor, a hardly believable claim. If your claim is accurate for the silicon, non-withstanding the CFA implementation, then there\'s more like 3.5-4.5 stops actually possible via alterations to the CFA, which we\'re seeing start to crop up now as the other limitations of Bayer become noticable. I don\'t expect that the 2x2 Bayer Matrix will remain the standard for more than a few more years now that the onboard processing power of most high-end cameras has reached a point where larger pixel arrays are viable.
Well, peak quantum efficiency is somewhere around 80%, I believe (it greatly depends on the wavelength and so is considerably less for red and blue) and there doesn\'t seem to be any reason to expect it to improve greatly in the near future.
Note that all our discussion about noise implies unchanging pixel density and so unchanging resolution. You can, of course, gain a lot of SNR by making pixels larger and sacrificing resolution for that. A mixed luminance/color filter array would do a very similar thing -- it would sacrifice color resolution to get better SNR. But this is not a pure win -- it\'s a trade-off. You will be able to get massively better SNR by ditching the CFA completely and making a luminance-only sensor (for a while B&W photographers had hopes for something like this) but this again is a different game.
Yet another way to improve SNR is to increase the transparency window of the CFA filters but there\'s a price here as well -- you \"muddy up\" the colors as you can\'t distinguish them as well now. It\'s a balancing act and another trade-off. Same thing for replacing the Bayer matrix with some other kind (e.g. Fuji\'s 3x3 matrix) -- you gain something, but you also lose something. TANSTAAFL, I\'m afraid.
What I think we\'ll see is clearer specialization -- some sensors will explicitly go for low noise and other sensors will go for other things, notably high resolution. But the easiest way to make this trade-off is still the simplest: change pixel density.
Feb 16, 2012 at 11:00 PM
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