You're welcome, Jon.


Quote Originally Posted by Jon Ruyle
I agree with all of this, assuming by “twice as bad” you mean snr is twice as bad, not absolute noise is twice as big
Yes, that's what I meant; I'm glad you saw through the obtuse writing.


One would naturally think that read noise must shrink in linear proportion to the area decrease in order to keep the same read noise. But the fact that noise adds in quadrature is what makes it possible for read noise to shrink at a slower rate while retaining the same "image level" noise (i.e. noise power for any given spatial frequency).

Quote Originally Posted by Jon Ruyle
Okay, so you're asserting that other things being equal, read noise is inversely proportional to the square root of the size of the pixel?
How about "read noise is directly proportional to the square area"? (e- / um^2.) I think that works.

Quote Originally Posted by Jon Ruyle
That this is true for photon noise is clearly true, and requires very little knowledge of how the camera works. That it is true for read noise seems less obvious to me, but I believe you
Read noise is indeed the much more complicated, inconsistant, and difficult to generalize. However, I think the rule is a pretty close fit to the cameras at hand. It's more often true for cameras of a similar sensor size and budget from the same manufacturer (e.g. 40D and 1D3), but not always. Unlike photon shot noise, read noise varies significantly from model to model, manufacturer to manufacturer, and even unit to unit of the same model. Generally, though, one of the exceptions seems to be that when comparing tiny inexpensive digicams to large, pricey DSLR, the DSLR has less read noise at high ISO, while the very tiny pixels in the cheap digicam have less read noise at low ISO. And yet high ISO read noise has dropped with each new and smaller pixel, and other DSLR seem to also indicate that it isn't something inherent to pixel size specifically, but another factor (design tradeoff?).

If we look at the example of the LX3 vs 5D2 at low ISO again:

5D2 6.4 microns vs LX3 2 microns using signal of 1 * N.
6.4um S/N = 23.5:23.5 (1:1)
2um scale factor = (6.4/2.0)^2 = 10.24
2um S = 23.5/10.24 = 2.2949
2um N = 5.6
2um S/N = 2.2949:5.6
2um resampled S = 2.30*10.24 = 23.5
2um resampled N = sqrt(5.6^2 * 10.24) = 17.92
2um resampled S/N = 23.5:17.92 = 1.31:1
31% better S/N.

Here's a visual example of a base ISO comparison that contains quite a bit of read noise (pushed from ISO 100 to ISO 13,000 in post).

http://forums.dpreview.com/forums/read.asp?forum=1018&message=28607494

Pattern noise is another important factor to consider. The 5D2, for example, has very strong and objectionable pattern noise. Yet even the inexpensive Canon digicams have no pattern noise. So while the RMS read noise number may indicate the 5D2 has a certain amount of read noise, it's actually worse than the indicated number because the pattern noise makes it objectionable to the eye.

It's also worth mentioning that the OLPF means that when the small pixels are resampled to the same pixel size as the large pixels, they will have more detail. In other words, for comparisons near the Nyquist frequency of the large pixels, small pixels have a big advantage in resolution and contrast. But if the desired spatial frequency is below the strongest effect of the AA filter, this difference is not relevant.

We have a lot to look forward to in the future.