What is the precise definition of signal to noise ratio, as used by DxOmark? Please see here, after clicking Measurements, SNR 18% (it's not directly linkable).
I am looking for an explanation (in particular a precise definition) which is understandable by someone who has sufficient mathematical background, but no familiarity with this engineering field and its conventions.
To put it differently, given a greyscale image
a_ij of a plain grey sheet (
a_ij representing the intensity at pixel location
(i,j)), how would one calculate the SNR? Also, does the calculation use the linear sensor data or the perceptual pixel values?