text: #!/usr/bin/env python
  ##########################################################################
  #
  # Copyright 2011 Jose Fonseca
  # Copyright 2008-2009 VMware, Inc.
  # All Rights Reserved.
  #
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be included in
  # all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  # THE SOFTWARE.
  #
  ##########################################################################/
  
  
  '''Snapshot (image) comparison script.
  '''
  
  
  import sys
  import os.path
  import optparse
  import math
  import operator
  
  from PIL import Image
  from PIL import ImageChops
  from PIL import ImageEnhance
  from PIL import ImageFilter
  
  
  thumbSize = 320
  
  gaussian_kernel = ImageFilter.Kernel((3, 3), [1, 2, 1, 2, 4, 2, 1, 2, 1], 16)
  
  class Comparer:
      '''Image comparer.'''
  
      def __init__(self, ref_image, src_image, alpha = False):
          if isinstance(ref_image, basestring):
              self.ref_im = Image.open(ref_image)
          else:
              self.ref_im = ref_image
  
          if isinstance(src_image, basestring):
              self.src_im = Image.open(src_image)
          else:
              self.src_im = src_image
  
          # Ignore
          if not alpha:
              self.ref_im = self.ref_im.convert('RGB')
              self.src_im = self.src_im.convert('RGB')
  
          self.diff = ImageChops.difference(self.src_im, self.ref_im)
  
      def size_mismatch(self):
          return self.ref_im.size != self.src_im.size
  
      def write_diff(self, diff_image, fuzz = 0.05):
          if self.size_mismatch():
              return
  
          # Make a difference image similar to ImageMagick's compare utility.
          #
          # Basically produces a brightened/faded version of the source image,
          # but where every pixel for which absolute error is larger than
          # 255*fuzz will be colored strong red.
  
          # Take the maximum error across all channels
          diff_max = reduce(ImageChops.lighter, self.diff.split())
  
          # Scale values so that pixels equal or above 255*fuzz become 255
          mask = diff_max.point(lambda x: min(x/fuzz, 255), 'L')
  
          lowlight = Image.new('RGB', self.src_im.size, (0xff, 0xff, 0xff))
          highlight = Image.new('RGB', self.src_im.size, (0xf1, 0x00, 0x1e))
          diff_im = Image.composite(highlight, lowlight, mask)
  
          diff_im = Image.blend(self.src_im, diff_im, 0xcc/255.0)
          diff_im.save(diff_image)
  
      def precision(self, filter=False):
          if self.size_mismatch():
              return 0.0
  
          diff = self.diff
          if filter:
              diff = diff.filter(gaussian_kernel)
  
          # See also http://effbot.org/zone/pil-comparing-images.htm
          h = diff.histogram()
          square_error = 0
          for i in range(1, 256):
              square_error += sum(h[i : 3*256: 256])*i*i
          rel_error = float(square_error*2 + 1) / float(self.diff.size[0]*self.diff.size[1]*3*255*255*2)
          bits = -math.log(rel_error)/math.log(2.0)
          return bits
  
      def ae(self, fuzz = 0.05):
          # Compute absolute error
  
          if self.size_mismatch():
              return sys.maxint
  
          # TODO: this is approximate due to the grayscale conversion
          h = self.diff.convert('L').histogram()
          ae = sum(h[int(255 * fuzz) + 1 : 256])
          return ae
  
  
  def surface(html, image):
      if True:
          name, ext = os.path.splitext(image)
          thumb = name + '.thumb' + ext
          if os.path.exists(image) \
             and (not os.path.exists(thumb) \
                  or os.path.getmtime(thumb) < os.path.getmtime(image)):
              im = Image.open(image)
              imageWidth, imageHeight = im.size
              if imageWidth <= thumbSize and imageHeight <= thumbSize:
                  if imageWidth >= imageHeight:
                      imageHeight = imageHeight*thumbSize/imageWidth
                      imageWidth = thumbSize
                  else:
                      imageWidth = imageWidth*thumbSize/imageHeight
                      imageHeight = thumbSize
                  html.write('        <td><img src="%s" width="%u" height="%u"/></td>\n' % (image, imageWidth, imageHeight))
                  return
  
              im.thumbnail((thumbSize, thumbSize))
              try:
                  im.save(thumb)
              except IOError:
                  thumb = image
      else:
          thumb = image
      html.write('        <td><a href="%s"><img src="%s"/></a></td>\n' % (image, thumb))
  
  
  def is_image(path):
      name = os.path.basename(path)
      name, ext1 = os.path.splitext(name)
      name, ext2 = os.path.splitext(name)
      return ext1 in ('.png', '.bmp') and ext2 not in ('.diff', '.thumb')
  
  
  def find_images(prefix):
      if os.path.isdir(prefix):
          prefix_dir = prefix
      else:
          prefix_dir = os.path.dirname(prefix)
  
      images = []
      for dirname, dirnames, filenames in os.walk(prefix_dir, followlinks=True):
          for filename in filenames:
              filepath = os.path.join(dirname, filename)
              if filepath.startswith(prefix) and is_image(filepath):
                  images.append(filepath[len(prefix):])
  
      return images
  
  
  def main():
      global options
  
      optparser = optparse.OptionParser(
          usage="\n\t%prog [options] <ref_prefix> <src_prefix>")
      optparser.add_option(
          '-v', '--verbose',
          action="store_true", dest="verbose", default=False,
          help="verbose output")
      optparser.add_option(
          '-o', '--output', metavar='FILE',
          type="string", dest="output", default='index.html',
          help="output filename [default: %default]")
      optparser.add_option(
          '-f', '--fuzz',
          type="float", dest="fuzz", default=0.05,
          help="fuzz ratio [default: %default]")
      optparser.add_option(
          '-a', '--alpha',
          action="store_true", dest="alpha", default=False,
          help="take alpha channel in consideration")
      optparser.add_option(
          '--overwrite',
          action="store_true", dest="overwrite", default=False,
          help="overwrite images")
      optparser.add_option(
          '--show-all',
          action="store_true", dest="show_all", default=False,
          help="show all images, including similar ones")
  
      (options, args) = optparser.parse_args(sys.argv[1:])
  
      if len(args) != 2:
          optparser.error('incorrect number of arguments')
  
      ref_prefix = args[0]
      src_prefix = args[1]
  
      ref_images = find_images(ref_prefix)
      src_images = find_images(src_prefix)
      images = list(set(ref_images).union(set(src_images)))
      images.sort()
  
      if options.output:
          html = open(options.output, 'wt')
      else:
          html = sys.stdout
      html.write('<html>\n')
      html.write('  <body>\n')
      html.write('    <table border="1">\n')
      html.write('      <tr><th>File</th><th>%s</th><th>%s</th><th>&Delta;</th></tr>\n' % (ref_prefix, src_prefix))
      failures = 0
      for image in images:
          ref_image = ref_prefix + image
          src_image = src_prefix + image
          root, ext = os.path.splitext(src_image)
          delta_image = "%s.diff.png" % (root, )
          if os.path.exists(ref_image) and os.path.exists(src_image):
              if options.verbose:
                  sys.stdout.write('Comparing %s and %s ...' % (ref_image, src_image))
              comparer = Comparer(ref_image, src_image, options.alpha)
              match = comparer.ae(fuzz=options.fuzz) == 0
              if match:
                  result = 'MATCH'
                  bgcolor = '#20ff20'
              else:
                  result = 'MISMATCH'
                  failures += 1
                  bgcolor = '#ff2020'
          else:
              comparer = None
              match = None
              result = 'MISSING'
              failures += 1
              bgcolor = '#ff2020'
  
          if options.verbose:
              sys.stdout.write(' %s\n' % (result,))
          html.write('      <tr>\n')
          html.write('        <td bgcolor="%s"><a href="%s">%s<a/></td>\n' % (bgcolor, ref_image, image))
          if not match or options.show_all:
              if comparer is not None \
                 and (options.overwrite \
                      or not os.path.exists(delta_image) \
                       or (os.path.getmtime(delta_image) < os.path.getmtime(ref_image) \
                           and os.path.getmtime(delta_image) < os.path.getmtime(src_image))):
                      comparer.write_diff(delta_image, fuzz=options.fuzz)
              surface(html, ref_image)
              surface(html, src_image)
              surface(html, delta_image)
          html.write('      </tr>\n')
          html.flush()
      html.write('    </table>\n')
      html.write('  </body>\n')
      html.write('</html>\n')
  
      if failures:
          sys.exit(1)
  
  if __name__ == '__main__':
      main()
  