tools/site_compare/operators/equals.py

   1 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 """Compare two images for equality."""
   6
   7 from PIL import Image
   8 from PIL import ImageChops
   9
  10
  11 def Compare(file1, file2, **kwargs):
  12   """Compares two images to see if they're identical.
  13
  14   Args:
  15     file1: path to first image to compare
  16     file2: path to second image to compare
  17     kwargs: unused for this operator
  18
  19   Returns:
  20     None if the images are identical
  21     A tuple of (errorstring, image) if they're not
  22   """
  23   kwargs = kwargs  # unused parameter
  24
  25   im1 = Image.open(file1)
  26   im2 = Image.open(file2)
  27
  28   if im1.size != im2.size:
  29     return ("The images are of different size (%s vs %s)" %
  30             (im1.size, im2.size), im1)
  31
  32   diff = ImageChops.difference(im1, im2)
  33
  34   if max(diff.getextrema()) != (0, 0):
  35     return ("The images differ", diff)
  36   else:
  37     return None