Noise can be assessed in uniform regions of an image, by subtracting a lowpass-filtered version of it. Then from the histogram of intensities, a global measure can be obtained (such as the average absolute deviation).
But do we have good means to determine noise intensity locally, on every pixel of an image, where the noise distribution varies per regions ?
(Note: we consider that random texturing of the surfaces as a noise.)
The noise we target is more of the Gaussian type.