im = imread('ctskull-256.tif');

im_requantizada = zeros(size(im));

subplot(3, 3, 1);
imshow(im);
for k = 1:7
  subplot(3, 3, k+1);
  maximo = (2**k - 1);
  for i = 1:size(im,1)
    for j = 1:size(im,2)
      im_requantizada(i,j) = double(round( double(im(i,j))*maximo / 255.0 )) / maximo;
    endfor
  endfor
  imshow(im_requantizada);
endfor