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 7 import logging 8 import os 9 import time 10 11 from PIL import ImageChops 12 13 14 class 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): 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 """ 36 # TODO(waihong): Support multiple capturers. 37 self._capturer1 = capturer1 38 self._capturer2 = capturer2 39 self._output_dir = output_dir 40 self._pixel_diff_margin = pixel_diff_margin 41 assert 0.0 <= wrong_pixels_margin <= 1.0 42 self._wrong_pixels_margin = wrong_pixels_margin 43 44 45 def compare(self): 46 """Compares the screens. 47 48 @return: None if the check passes; otherwise, a string of error message. 49 """ 50 tags = [self._capturer1.TAG, self._capturer2.TAG] 51 images = [self._capturer1.capture(), self._capturer2.capture()] 52 53 if None in images: 54 message = ('Failed to capture the screen of %s.' % 55 tags[images.index(None)]) 56 logging.error(message) 57 return message 58 59 # Sometimes the format of images got from X is not RGB, 60 # which may lead to ValueError raised by ImageChops.difference(). 61 # So here we check the format before comparing them. 62 for i, image in enumerate(images): 63 if image.mode != 'RGB': 64 images[i] = image.convert('RGB') 65 66 message = 'Unexpected exception' 67 time_str = time.strftime('%H%M%S') 68 try: 69 # The size property is the resolution of the image. 70 if images[0].size != images[1].size: 71 message = ('Sizes of images %s and %s do not match: ' 72 '%dx%d != %dx%d' % 73 (tuple(tags) + images[0].size + images[1].size)) 74 logging.error(message) 75 return message 76 77 size = images[0].size[0] * images[0].size[1] 78 max_acceptable_wrong_pixels = int(self._wrong_pixels_margin * size) 79 80 logging.info('Comparing the images between %s and %s...', *tags) 81 diff_image = ImageChops.difference(*images) 82 histogram = diff_image.convert('L').histogram() 83 84 num_wrong_pixels = sum(histogram[self._pixel_diff_margin + 1:]) 85 max_diff_value = max(filter( 86 lambda x: histogram[x], xrange(len(histogram)))) 87 if num_wrong_pixels > 0: 88 logging.debug('Histogram of difference: %r', histogram) 89 prefix_str = '%s-%dx%d' % ((time_str,) + images[0].size) 90 message = ('Result of %s: total %d wrong pixels ' 91 '(diff up to %d)' % ( 92 prefix_str, num_wrong_pixels, max_diff_value)) 93 if num_wrong_pixels > max_acceptable_wrong_pixels: 94 logging.error(message) 95 return message 96 97 message += (', within the acceptable range %d' % 98 max_acceptable_wrong_pixels) 99 logging.warning(message) 100 else: 101 logging.info('Result: all pixels match (within +/- %d)', 102 max_diff_value) 103 message = None 104 return None 105 finally: 106 if message is not None: 107 for i in (0, 1): 108 # Use time and image size as the filename prefix. 109 prefix_str = '%s-%dx%d' % ((time_str,) + images[i].size) 110 # TODO(waihong): Save to a better lossless format. 111 file_path = os.path.join( 112 self._output_dir, 113 '%s-%s.png' % (prefix_str, tags[i])) 114 logging.info('Output the image %d to %s', i, file_path) 115 images[i].save(file_path) 116 117 file_path = os.path.join( 118 self._output_dir, '%s-diff.png' % prefix_str) 119 logging.info('Output the diff image to %s', file_path) 120 diff_image = ImageChops.difference(*images) 121 gray_image = diff_image.convert('L') 122 bw_image = gray_image.point( 123 lambda x: 0 if x <= self._pixel_diff_margin else 255, 124 '1') 125 bw_image.save(file_path) 126
