MATLAB: Overcome for loops for fast processing

MATLAB

I have the following part of MATLAB code
skin_rgb = zeros(256.^3,1);
for i = [2000 : 2003,2008,2010:2011,2013:2015,2017:2018,2021,2024,2027:2041,2043,2045:2059,2061:2063]
    I = imread(['skin_img',num2str(i),'.tif']);
         [x,y,~]= size(I);
         for l = 1:x
             for j = 1:y
                  if (I(l,j,1) ~= 255 && I(l,j,2) ~= 255 && I(l,j,3) ~= 255)
                     aa = double([I(l,j,1) , I(l,j,2) , I(l,j,3)]);
                     [~,ee1] = ismember(aa,rgb_hist,'rows');
                     skin_rgb(ee1) = skin_rgb(ee1) + 1; 
                     b1 = b1 + 1;
                 end
             end
         end
end
The output of the code is perfect. The issue is it is very slow. Inside the if loop the size of rgb_hist variable is 255.^3 x 3. Is there any way to get rid of the two nested for loops? As I am doing Image processing on high resolution image the variable x and y (different for each "i" iteration) have a big number in it.
Thank you

Best Answer

skin_rgb = 0;
for i = [2000 : 2003,2008,2010:2011,2013:2015,2017:2018,2021,2024,2027:2041,2043,2045:2059,2061:2063]
    I = imread(['skin_img',num2str(i),'.tif']);
    RGB = reshape(double(I),[],3)+1;
    skin_rgb = skin_rgb + accumarray(RGB,1,256+[0 0 0]);
end
skin_rgb = permute(skin_rgb,[3 2 1]);
skin_rgb = skin_rgb(:);
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