title: ImageChops.difference not working with simple png images
body: <p>I am creating a simple script to check if images are the same or different.</p>
  <p>My code works for the jpg files but not for the png files.</p>
  <p>For some reason, my code below thinks that the below png:</p>
  <p><a href="https://i.stack.imgur.com/Sug2X.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Sug2X.png" alt="enter image description here" /></a></p>
  <p>is the same as below png</p>
  <p><a href="https://i.stack.imgur.com/tWvnL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tWvnL.png" alt="enter image description here" /></a></p>
  <pre><code>from PIL import Image, ImageChops
  
  
  img1 = Image.open('./1.png')
  img2 = Image.open('./2.png')
  
  img3 = Image.open('./A.jpg')
  img4 = Image.open('./B.jpg')
  diff1 = ImageChops.difference(img3, img4)
  diff = ImageChops.difference(img2, img1)
  
  print(diff.getbbox())
  if diff.getbbox():
      diff.show() # does not work for me. should show image if they are different
  
  print(diff1.getbbox())
  
  if diff1.getbbox():
      diff1.show() # this works not sure why the PNG files do not
  </code></pre>
  <p>I am running this on Ubuntu. I am not sure what I am doing wrong. Any help would be great thanks!</p>
  <p><strong>Working code after @Mark's help</strong>: <a href="https://github.com/timothy/image_diff/blob/master/test.py" rel="nofollow noreferrer">https://github.com/timothy/image_diff/blob/master/test.py</a></p>