f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
xpatUSA
xpatUSA Forum Pro • Posts: 10,924
Re: SNAP! Where it is?

dwalby wrote:

From what I gather so far, the SNR improvement in these two cases seems to be achieved through pixel binning, either directly or by your eye's perception. I believe the actual SNR of each recorded pixel is the same, as they are the same pixel with the same illuminance in both cases. So the only way one can become less noisy is if some additional processing is performed, and that would be binning because one image contains 4x (or whatever multiple) pixels compared to the other. Its analogous to having a pixel that's 4x larger and collects 4x the photons, thus has a better SNR.

When you bin, the processing advantage only applies if the noise samples are uncorrelated, which they are at native resolution. If you upsample the smaller image to the larger image pixel count, your noise samples after upsampling are no longer uncorrelated. Therefore if you later bin both images, one will enjoy the sqrt(N) SNR improvement, and the other will not, because the larger one has uncorrelated noise samples and the (upsampled) smaller one does not.

Sigma cameras do binning right there on the sensor chip. Actual photodiode output are joined together. By this means the capacitances are placed in parallel. So, 4X the electrons are produced but they go into 4X the capacitance. In other words, simple averaging with a sqrt(N) improvement in SNR.

However, an unbinned image from my Sigma, re-sampled 50% , is 'better' because of an increase in contrast, plus the use of almost any modern re-sampling method (bicubic, Lanczos) is superior to simple averaging.

Just a comment really, how it relates to upsizing I have no idea - never do it, myself.

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Cheers,
Ted

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