MATLAB Answers

Calculate mean of gray Value

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arame sotudegan
arame sotudegan on 31 Mar 2021
Answered: Chad Greene on 31 Mar 2021
Hello, In this picture I want to calculate mean of the circle. but when I use mean( ) it calculates all the pixels including the black ones, so the mean value decreases. Is there a way to calculate only the gray value?
Thank you in advance.

Accepted Answer

DGM
DGM on 31 Mar 2021
Edited: DGM on 31 Mar 2021
Something like this:
% mean of non-black regions
mean(mypicture(mypicture>0))
This assumes that the image background is actually zero; otherwise, you can test that it's above some threshold value

More Answers (1)

Chad Greene
Chad Greene on 31 Mar 2021
Try this. Below I'm creating an example matrix M, and calculate the mean of only the values that exceed zero:
M = peaks(100); % example matrix
M(M<=0) = 0;
figure
imagesc(M)
colormap(gray)
colorbar
mask = M>0; % logical mask corresponding to all values greater than zero
figure
imagesc(mask)
mean(M(mask),'all') % mean of all values of M that exceed zero.
ans = 1.1528

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