MATLAB: I have tried the coding. But i don’t understand what does mean idx = Igray == 0? Can someone explain it to me.

rgb

if true
  % code
endSeparate to RGB channel
Ir = imgcrop(:,:,1);
Ig = imgcrop(:,:,2);
Ib = imgcrop(:,:,3);
% Extract the background (black) region
Igray = rgb2gray(imgcrop);
idx = Igray == 0;
% Calculate average RGB of the region
Rave = uint8(mean(Ir(~idx)));
Gave = uint8(mean(Ig(~idx)));
Bave = uint8(mean(Ib(~idx)));

Best Answer

This code is calculating the average of RGB channels while excluding the pixels where the intensity level is zero.
The line
idx = Igray == 0;
find all the pixels in grayscale image Igray, where the intensity is 0. It will return a logical matrix idx. Since only those pixels are required where intensity level is not 0, therefore we invert the logical matrix using ~idx,
Ir(~idx)
will return all the required pixels and then using mean() find the average. See Logical Indexing here.
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