Median gray level value

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Faraz
Faraz 2011-11-25
Hi there,
How can I find the median gray level of non-zero valued pixels in an image?
I am working on mammograms that have lot of zero valued pixels, but it dosent matter.
Thanks

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Sven
Sven 2011-11-25
Hi Faraz, you can simply make a mask of the pixels you don't want to include, then take the median of all the others:
Im = randi(10,512,512) - 1; % Sample image with some 0s
zeroMask = Im==0; % Mask of 0s
medValue = median(Im(~zeroMask)) % Median of the rest
Or, in one command:
medValue = median(Im(Im>0));

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Image Analyst
Image Analyst 2011-11-25
Use logical indexing. See this demo:
% Generate some sample data.
A = [1 2 4 4; 3 0 6 6; 5 0 8 8; 5 6 8 0]
% Just FYI, let's see what we're going to use
AZ = A > 0
% Normal median value
medianValue = median(A(:))
% Now get the median of where A>0
medianValue = median(A(A>0))

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