#!/usr/bin/env python
# $URL: http://pypng.googlecode.com/svn/trunk/code/pipcolours $
# $Rev: 96 $

# pipcolours - extract all colours present in source image.

def colours(out, inp):
    import itertools
    import png

    r = png.Reader(file=inp)
    _,_,pixels,info = r.asDirect()
    planes = info['planes']
    col = set()
    for row in pixels:
        # Ewgh, side effects on col
        map(col.add, png.group(row, planes))
    col,planes = channel_reduce(col, planes)
    col = list(col)
    col.sort()
    col = list(itertools.chain(*col))
    width = len(col)//planes
    greyscale = planes in (1,2)
    alpha = planes in (2,4)
    bitdepth = info['bitdepth']
    w = png.Writer(width, 1,
        bitdepth=bitdepth, greyscale=greyscale, alpha=alpha)
    w.write(out, [col])

def channel_reduce(col, planes):
    """Attempt to reduce the number of channels in the set of
    colours."""
    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 main(argv=None):
    import sys

    if argv is None:
        argv = sys.argv

    argv = argv[1:]
    if len(argv) > 0:
        f = open(argv[0], 'rb')
    else:
        f = sys.stdin
    return colours(sys.stdout, f)

if __name__ == '__main__':
    main()