The Joy of Pixel Density

Started Jul 13, 2008 | Discussions thread
Tristan Cope Senior Member • Posts: 1,141
Re: Shot noise

aclo wrote:

Tristan Cope wrote:

If the photon count
for each individual pixel gets very low, then then signal to noise
ration dramatically falls.

Let say, for example that we have a 40MP 1/1.8 sensor, and that in
certain light conditions the average photon count per pixel is aound
1. Because of the effect of shot noise the signal will be
indistinguishable from the noise. Binning pixels won't help.

The last statement isn't true. Can you explain the thinking that
leads to it?

Yes. Lets take the extreme case and say that one photon is falling on each sensor element. Signal = 1, noise = sqrt 1 = 1. Signal and noise are equal (essentially photon flux per sensor element is entirely random regardless of the signal). This is a quantum effect.

"Binning can be done in firmware after signal readout and amplification, but this wouldn't reduce shot noise. To bin sensor elements together in a way that reduced shot noise would require this to be done in hardware at sensor level before readout. 2x2 (or 4x4) blocks blocks of immediately adjacent sensor elements would have to be combined before readout so they were treated as a single large sensor element (i.e. a bigger "pixel"). This can't be done with CFA sensors due to the CFA array. You would be binning pixels with different colour information.

I don't think on-sensor hardware binning is something that can be easily accomplished with CFA sensors (unlike monochrome sensors). If it was, all the manufacturers would be doing it. Here is Kodaks latest effort using panchromatic elements:
http://johncompton.pluggedin.kodak.com/default.asp?item=624876

Is there any CFA camera on the market currently that claims to use hardware pixel binning?

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I just like the pictures.

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