MATLAB: I assign A = B; but I could not use A and B interchangeably

digital image processingimage processingMATLAB

Hi everyone,
I'm trying to make a 3D median filter for a 3D CT image, here is my code:
function I_fted = abc(img, mar)
I_fted = img;
% For-loop to loop through each pixel in x,y,z directions and filtration
for y = 1+mar:size(img,1)-mar                    %loop through the vertical direction
    for x = 1+mar:size(img,2)-mar                %loop through the horizontal direction
        for z = 1+mar:size(img,3)-mar            %loop through the slices
            grid = img(y-mar:y+mar, x-mar:x+mar,z-mar:z+mar);     %create a cubic grid [mar x mar x mar]
            I_fted(y,x,z) = median(grid(:));        %calculate the median of the pixels inside cubic grid
        end
    end
end
end
I did assign I_fted = img. However, when I use the below commands, the result images are different for each case. I don't know why
% Case 1:
grid = img(y-mar:y+mar, x-mar:x+mar,z-mar:z+mar);        %this give different result to the below
% Case 2:
grid = I_fted(y-mar:y+mar, x-mar:x+mar,z-mar:z+mar);

Best Answer

You are changing I_fted inside the loop. If you subsequently use it in another calculation within the loop, it would not be surprising that the results are different from what you would get using img, which was not changed within the loop.
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