The Joy of Pixel Density

Started Jul 13, 2008 | Discussions thread
GordonBGood Veteran Member • Posts: 6,308
Re: Shot noise

Tristan Cope wrote:

This is what I was trying to get at with my post. 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.
Sufficient photons per pixel are required to statistically
distinguish signal from noise.

This would still be the case even if there was no read noise.

No, binning photosites would help. For the situation you describe above, by binning four photosites together the total number of electrons would go to four but the noise by the square root of the number of electrons would be two, so you would have a 2:1 Signal to Noise Ratio (SNR) or twice as good as not binning. I am not considering read noise, just as you say.

Regards, GordonBGood

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