screenshot.py 文件源码

def equal(self, img1, img2, skip_area=None):
        """Compares two screenshots using Root-Mean-Square Difference (RMS).
        @param img1: screenshot to compare.
        @param img2: screenshot to compare.
        @return: equal status.
        """
        if not HAVE_PIL:
            return None

        # Trick to avoid getting a lot of screen shots only because the time in the windows
        # clock is changed.
        # We draw a black rectangle on the coordinates where the clock is locates, and then
        # run the comparison.
        # NOTE: the coordinates are changing with VM screen resolution.
        if skip_area:
            # Copying objects to draw in another object.
            img1 = img1.copy()
            img2 = img2.copy()
            # Draw a rectangle to cover windows clock.
            for img in (img1, img2):
                self._draw_rectangle(img, skip_area)

        # To get a measure of how similar two images are, we use
        # root-mean-square (RMS). If the images are exactly identical,
        # this value is zero.
        diff = ImageChops.difference(img1, img2)
        h = diff.histogram()
        sq = (value * ((idx % 256)**2) for idx, value in enumerate(h))
        sum_of_squares = sum(sq)
        rms = math.sqrt(sum_of_squares/float(img1.size[0] * img1.size[1]))

        # Might need to tweak the threshold.
        return rms < 8