2022-09-19 03:25:22 +00:00
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#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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"""
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Usage: python palfix.py image.png
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2023-11-21 00:05:09 +00:00
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Fix the palette format of the input image to two-bit grayscale.
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Colored images will have their palette sorted {white, light
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color, dark color, black}.
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2022-09-19 03:25:22 +00:00
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"""
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import sys
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import png
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def rgb8_to_rgb5(c):
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r, g, b = c
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return (r // 8, g // 8, b // 8)
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def invert(c):
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r, g, b = c
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return (31 - r, 31 - g, 31 - b)
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def luminance(c):
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r, g, b = c
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return 0.299 * r**2 + 0.587 * g**2 + 0.114 * b**2
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def rgb5_pixels(row):
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yield from (rgb8_to_rgb5(row[x:x+3]) for x in range(0, len(row), 4))
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def fix_pal(filename):
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with open(filename, 'rb') as file:
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width, height, rows = png.Reader(file).asRGBA8()[:3]
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rows = list(rows)
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b_and_w = {(0, 0, 0), (31, 31, 31)}
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colors = {c for row in rows for c in rgb5_pixels(row)} - b_and_w
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if not colors:
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colors = {(21, 21, 21), (10, 10, 10)}
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elif len(colors) == 1:
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c = colors.pop()
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colors = {c, invert(c)}
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elif len(colors) != 2:
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return False
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palette = tuple(sorted(colors | b_and_w, key=luminance, reverse=True))
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assert len(palette) == 4
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2023-11-21 00:05:09 +00:00
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rows = [[3 - palette.index(c) for c in rgb5_pixels(row)] for row in rows]
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writer = png.Writer(width, height, greyscale=True, bitdepth=2, compression=9)
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2022-09-19 03:25:22 +00:00
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with open(filename, 'wb') as file:
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writer.write(file, rows)
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return True
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def main():
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if len(sys.argv) < 2:
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print(f'Usage: {sys.argv[0]} pic.png', file=sys.stderr)
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sys.exit(1)
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for filename in sys.argv[1:]:
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if not filename.lower().endswith('.png'):
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print(f'{filename} is not a .png file!', file=sys.stderr)
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elif not fix_pal(filename):
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print(f'{filename} has too many colors!', file=sys.stderr)
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if __name__ == '__main__':
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main()
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