| 1 | #!/usr/bin/env python |
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| 2 | |
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| 3 | import sys |
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| 4 | import png |
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| 5 | import array |
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| 6 | |
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| 7 | def usage(): |
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| 8 | return """%s <file1.png> <file2.png>""" % sys.argv[0] |
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| 9 | |
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| 10 | def rgb2rgba(px, w, h): |
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| 11 | npx = array.array('B') |
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| 12 | nbytes = w * h * 3 |
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| 13 | i = 0 |
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| 14 | while i < nbytes: |
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| 15 | npx.append(px[i]) |
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| 16 | npx.append(px[i+1]) |
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| 17 | npx.append(px[i+2]) |
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| 18 | npx.append(255) |
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| 19 | i = i + 3 |
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| 20 | return npx |
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| 21 | |
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| 22 | class Buffer: |
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| 23 | def __init__(self, w, h, px, format): |
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| 24 | self.width = w |
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| 25 | self.height = h |
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| 26 | if format == "rgb": |
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| 27 | self.pixels = rgb2rgba(px, w, h) |
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| 28 | else: |
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| 29 | self.pixels = px |
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| 30 | self.bpp = 4 # bytes per pixel |
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| 31 | |
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| 32 | def npixels(self): |
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| 33 | return self.width * self.height |
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| 34 | |
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| 35 | def nbytes(self): |
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| 36 | return self.npixels() * self.bpp |
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| 37 | |
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| 38 | def compute_histogram(self): |
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| 39 | hists = [[0 for x in xrange(256)] for y in range(self.bpp)] |
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| 40 | nbytes = self.nbytes() |
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| 41 | px = self.pixels |
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| 42 | stride = self.bpp |
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| 43 | imsize = self.nbytes() |
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| 44 | for channel in range(self.bpp): |
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| 45 | hist = hists[channel] |
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| 46 | i = channel |
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| 47 | while i < imsize: |
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| 48 | value = px[i] |
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| 49 | hist[value] += 1 |
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| 50 | i = i + stride |
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| 51 | return hists |
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| 52 | |
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| 53 | def rgba_mse(b1, b2, offset): |
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| 54 | imsize = b1.nbytes() |
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| 55 | mse = 0.0 |
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| 56 | p1 = b1.pixels |
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| 57 | p2 = b2.pixels |
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| 58 | stride = b1.bpp |
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| 59 | while offset < imsize: |
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| 60 | diff = p1[offset] - p2[offset] |
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| 61 | mse += diff * diff |
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| 62 | offset += stride |
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| 63 | return mse / b1.npixels() |
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| 64 | |
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| 65 | def msecompare(b1, b2): |
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| 66 | return [rgba_mse(b1, b2, c) for c in xrange(4)] |
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| 67 | |
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| 68 | def histcompare(b1, b2): |
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| 69 | h1 = b1.compute_histogram() |
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| 70 | h2 = b2.compute_histogram() |
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| 71 | diffs = [0, 0, 0, 0] |
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| 72 | for c in xrange(len(h1)): |
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| 73 | c1 = h1[c] |
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| 74 | c2 = h2[c] |
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| 75 | d = diffs[c] |
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| 76 | for v in xrange(len(c1)): |
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| 77 | d = d + abs(c1[v] - c2[v]) |
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| 78 | diffs[c] = d |
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| 79 | return diffs |
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| 80 | |
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| 81 | def format_from_pngmetadata(m): |
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| 82 | if m['has_alpha']: |
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| 83 | return "rgba" |
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| 84 | else: |
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| 85 | return "rgb" |
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| 86 | |
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| 87 | if __name__ == "__main__": |
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| 88 | if len(sys.argv) < 3: |
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| 89 | print usage() |
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| 90 | sys.exit(1) |
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| 91 | |
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| 92 | file1 = sys.argv[1] |
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| 93 | file2 = sys.argv[2] |
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| 94 | w1, h1, p1, m1 = png.Reader(file1).read() |
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| 95 | w2, h2, p2, m2 = png.Reader(file2).read() |
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| 96 | b1 = Buffer(w1, h1, p1, format_from_pngmetadata(m1)) |
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| 97 | b2 = Buffer(w2, h2, p2, format_from_pngmetadata(m2)) |
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| 98 | print msecompare(b1, b2) |
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| 99 | print histcompare(b1, b2) |
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