Quote:
Originally Posted by RickS
Sorry Andrew, I'm not convinced. Ignoring inconvenient practical issues like read noise, whether I collect and integrate exactly the same stream of photons in a single exposure or across multiple exposures with the same total length I get exactly the same data in the end.
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Well, not the same data, as the noise is higher in a single exposure than in stacked exposures.
I think from memory that if you stack two signal that the noise goes down by the root of 2.
*edit* found it here:
Quote:
The more images you take the further the random noise will be reduced relative to the signal. If the signal to noise ratio of one image is λ/sqrt(λ) then the signal to noise ratio of the ensemble average is λ/(sqrt(λ)/sqrt(n)) where n is the number of images in the ensemble. In other words, since noise sums in quadrature the noise in an average of n images is reduced by the sqrt(n) compared to the noise in a single image.
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source:
http://jethomson.wordpress.com/spect...ise-reduction/
Which is why, as Andrew points out, you can't stack the same image multiple times to reduce noise.