I'm currently using code:
i = imread('/usr/share/icons/matlab.png'); for k=1:1:m for l=1:1:n %a(k,l)=m*n; a(k,l) = (.299*i(k,l,1))+(.587*i(k,l,2))+(.114*i(k,l,3)); end end imshow(a); It shows only a white screen. Also the newly generated dimensions are n x m x 3 whereas it should be only m x n x 1.
If I use mat2gray it display the image like this
Since the image is a PNG, imread() is returning an integer image, with intensity values in the range [0 255] or equivalent, depending on the original bit depth. The conversion formula makes a a double image, which is expected to have intensities in the range [0 1]. Since all the pixel values in a are probably much greater than 1, they get clipped to 1 (white) by imshow().
The best option is to explicitly convert the image format before you start - this will take care of scaling things correctly:
i = imread('/usr/share/icons/matlab.png'); i = im2double(i); a = .299*i(:,:,1) + .587*i(:,:,2) + .114*i(:,:,3); % no need for loops imshow(a);