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#!/usr/bin/env python
"""
pipcolours - extract all colours present in source image.
Produces a PNG that has each colour exactly once.
Also performs grey and alpha reduction when possible:
if all colour pixels are grey, output PNG is grey;
if all pixels are opaque, output PNG has no alpha channel.
"""
import sys
def colours(out, inp):
import itertools
import png
r = png.Reader(file=inp)
_,_,pixels,info = r.asDirect()
planes = info['planes']
bitdepth = info['bitdepth']
col = set()
for row in pixels:
col = col.union(png.group(row, planes))
col, planes = channel_reduce(col, planes, bitdepth)
col = sorted(col)
col = list(itertools.chain(*col))
width = len(col) // planes
greyscale = planes in (1,2)
alpha = planes in (2,4)
w = png.Writer(width, 1,
bitdepth=bitdepth, greyscale=greyscale, alpha=alpha)
w.write(out, [col])
def channel_reduce(col, planes, bitdepth):
"""Attempt to reduce the number of channels in the set of colours."""
col, planes = reduce_grey(col, planes)
col, planes = reduce_alpha(col, planes, bitdepth)
return col, planes
def reduce_grey(col, planes):
"""
Reduce a colour image to grey if
all intensities match in all pixels.
"""
if planes >= 3:
def isgrey(c):
return c[0] == c[1] == c[2]
if min(map(isgrey, col)) == True:
# Every colour is grey.
col = set(map(lambda x: x[0::3], col))
planes -= 2
return col, planes
def reduce_alpha(col, planes, bitdepth):
"""
Remove alpha channel if all pixels are fully opaque.
"""
maxval = 2 ** bitdepth - 1
if planes in (2, 4):
def isopaque(c):
return c[-1] == maxval
if min(map(isopaque, col)) == True:
# Every pixel is opaque
col = set(map(lambda x: x[:-1], col))
planes -= 1
return col, planes
def ensure_binary_stdin():
"""
Ensure sys.stdin returns bytes.
"""
try:
# Ensure sys.stdin returns bytes
sys.stdin = sys.stdin.buffer
except AttributeError:
# Probably Python 2, where bytes are strings.
pass
def ensure_binary_stdout():
"""
Ensure sys.stdout accepts bytes.
"""
# First there is a Python3 issue.
try:
sys.stdout = sys.stdout.buffer
except AttributeError:
# Probably Python 2, where bytes are strings.
pass
# On Windows the C runtime file orientation needs changing.
if sys.platform == "win32":
import msvcrt
import os
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
def main(argv=None):
if argv is None:
argv = sys.argv
argv = argv[1:]
if len(argv) > 0:
f = open(argv[0], 'rb')
else:
ensure_binary_stdin()
f = sys.stdin
ensure_binary_stdout()
return colours(sys.stdout, f)
if __name__ == '__main__':
main()
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