Nikon finally gets the noise down.

Started Nov 17, 2007 | Discussions thread
alanr0 Senior Member • Posts: 2,164
Re: How to subtract in quadrature?

Bill Janes wrote:

A very interesting analysis, but one thing I don't understand is
subtracting in quadrature. Can someone explain this?

The assumption is that photon noise (P) and readout noise (R) are uncorrelated. In this case the total noise variance is the sum of the variances of photon and readout noises. The RMS noise (N) is therefore given by the square root of the sum of variances. The two components add in quadrature.
N = sqrt(P^2 + R^2)

We need the photon noise variance to estimate the quantum efficiency. We estimate this by subtracting the read-out variance from the total noise variance. This is what is meant by subtracting in quadrature.
P^2 = N^2 - R^2

Alan Robinson

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