The argument above provides a method to compare cameras with
different resolutions. A high-resolution camera can still be
turned into a low-resolution camera by averaging its pixels.
order to compare all cameras and not just pairs, a reference
resolution can be chosen and equivalent SNRs at this resolution
are computed. Let Nref denote this reference resolution.
Consider a camera with N Mpix. To obtain an image with Nref
pixels, N / Nref pixels need to be averaged out to produce a
single pixel in the output image, so the noise decreases by a
factor of . We then deduce that SNRref at resolution Nref can be
obtained from the nominal SNR (in dB) using the formula Notice
that if the reference resolution Nref is very large, or if the
initial sensor has a low resolution, the normalized SNR can
actually be lower than the nominal SNR.