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1# Copyright 2014 The Chromium OS 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"""Classes to do screen comparison."""
6
7import logging
8import os
9import time
10
11from PIL import ImageChops
12
13
14class ScreenComparer(object):
15    """A class to compare two screens.
16
17    Calling its member method compare() does the comparison.
18
19    """
20
21    def __init__(self, capturer1, capturer2, output_dir, pixel_diff_margin,
22                 wrong_pixels_margin, skip_if_diff_sizes=False):
23        """Initializes the ScreenComparer objects.
24
25        @param capture1: The screen capturer object.
26        @param capture2: The screen capturer object.
27        @param output_dir: The directory for output images.
28        @param pixel_diff_margin: The margin for comparing a pixel. Only
29                if a pixel difference exceeds this margin, will treat as a wrong
30                pixel. Sets None means using default value by detecting
31                connector type.
32        @param wrong_pixels_margin: The percentage of margin for wrong pixels.
33                The value is in a closed interval [0.0, 1.0]. If the total
34                number of wrong pixels exceeds this margin, the check fails.
35        @param skip_if_diff_sizes: Skip the comparison if the image sizes are
36                different. Used in mirrored test as the internal and external
37                screens have different resolutions.
38        """
39        # TODO(waihong): Support multiple capturers.
40        self._capturer1 = capturer1
41        self._capturer2 = capturer2
42        self._output_dir = output_dir
43        self._pixel_diff_margin = pixel_diff_margin
44        assert 0.0 <= wrong_pixels_margin <= 1.0
45        self._wrong_pixels_margin = wrong_pixels_margin
46        self._skip_if_diff_sizes = skip_if_diff_sizes
47
48
49    def compare(self):
50        """Compares the screens.
51
52        @return: None if the check passes; otherwise, a string of error message.
53        """
54        tags = [self._capturer1.TAG, self._capturer2.TAG]
55        images = [self._capturer1.capture(), self._capturer2.capture()]
56
57        if None in images:
58            message = ('Failed to capture the screen of %s.' %
59                       tags[images.index(None)])
60            logging.error(message)
61            return message
62
63        # Sometimes the format of images got from X is not RGB,
64        # which may lead to ValueError raised by ImageChops.difference().
65        # So here we check the format before comparing them.
66        for i, image in enumerate(images):
67          if image.mode != 'RGB':
68            images[i] = image.convert('RGB')
69
70        message = 'Unexpected exception'
71        time_str = time.strftime('%H%M%S')
72        try:
73            # The size property is the resolution of the image.
74            if images[0].size != images[1].size:
75                message = ('Sizes of images %s and %s do not match: '
76                           '%dx%d != %dx%d' %
77                           (tuple(tags) + images[0].size + images[1].size))
78                if self._skip_if_diff_sizes:
79                    logging.info(message)
80                    return None
81                else:
82                    logging.error(message)
83                    return message
84
85            size = images[0].size[0] * images[0].size[1]
86            max_acceptable_wrong_pixels = int(self._wrong_pixels_margin * size)
87
88            logging.info('Comparing the images between %s and %s...', *tags)
89            diff_image = ImageChops.difference(*images)
90            histogram = diff_image.convert('L').histogram()
91
92            num_wrong_pixels = sum(histogram[self._pixel_diff_margin + 1:])
93            max_diff_value = max(filter(
94                    lambda x: histogram[x], xrange(len(histogram))))
95            if num_wrong_pixels > 0:
96                logging.debug('Histogram of difference: %r', histogram)
97                prefix_str = '%s-%dx%d' % ((time_str,) + images[0].size)
98                message = ('Result of %s: total %d wrong pixels '
99                           '(diff up to %d)' % (
100                           prefix_str, num_wrong_pixels, max_diff_value))
101                if num_wrong_pixels > max_acceptable_wrong_pixels:
102                    logging.error(message)
103                    return message
104
105                message += (', within the acceptable range %d' %
106                            max_acceptable_wrong_pixels)
107                logging.warning(message)
108            else:
109                logging.info('Result: all pixels match (within +/- %d)',
110                             max_diff_value)
111            message = None
112            return None
113        finally:
114            if message is not None:
115                for i in (0, 1):
116                    # Use time and image size as the filename prefix.
117                    prefix_str = '%s-%dx%d' % ((time_str,) + images[i].size)
118                    # TODO(waihong): Save to a better lossless format.
119                    file_path = os.path.join(
120                            self._output_dir,
121                            '%s-%s.png' % (prefix_str, tags[i]))
122                    logging.info('Output the image %d to %s', i, file_path)
123                    images[i].save(file_path)
124
125                file_path = os.path.join(
126                        self._output_dir, '%s-diff.png' % prefix_str)
127                logging.info('Output the diff image to %s', file_path)
128                diff_image = ImageChops.difference(*images)
129                gray_image = diff_image.convert('L')
130                bw_image = gray_image.point(
131                        lambda x: 0 if x <= self._pixel_diff_margin else 255,
132                        '1')
133                bw_image.save(file_path)
134