title: Matlab imwrite function changes the pixel values
body: <p>I tried to change some pixel values of a Grayscale image and save it using imwrite in matlab.
  no problem with saving.
  the problem is when I read it back, some pixel values have been changed. not exactly the same values I assigned to pixels before saving it.
  I'm trying to hash images so 1unit difference will effect the hash numbers.</p>