Median gray level value

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

Answer 1

[Sven]

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));

[Faraz]

Thanks Sven

Answer 2

[Image Analyst]

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))

[Faraz]

Thanks Image analyst