title: matlab, images are the same size but I can't use imabsdiff
body: <p>I want to use <strong>imabsdiff</strong> in matlab to find the difference between two images.
  when I use it I have this error on the terminal (X and Y are the images) </p>
  
  <blockquote>
    <p>X and Y must be the same size.</p>
  </blockquote>
  
  <p>but my problem is that when I use <strong>size</strong> function for checking the size of images one of them is <em>512, 512</em> and another one is <em>512, 512, 3</em></p>
  
  <p>I have no idea about this, what should I do? :(</p>
  
  <p>thanks in advance :)</p>