code/pripalpng

#!/usr/bin/env python
# pripalpng


"""Convert to Palette PNG (without changing colours)"""

import argparse
import collections

# https://docs.python.org/2.7/library/io.html
import io
import string
import zlib

# Local module.
import png


def make_inverse_palette(rows, channels):
    """
    The inverse palette maps from tuple to palette index.
    """

    palette = {}

    for row in rows:
        for pixel in png.group(row, channels):
            if pixel in palette:
                continue
            palette[pixel] = len(palette)
    return palette


def palette_convert(out, inp, palette_file):
    """
    Convert PNG image in `inp` to use a palette, colour type 3,
    and write converted image to `out`.

    `palette_file` is a file descriptor for the palette to use.

    If `palette_file` is None, then `inp` is used as the palette.
    """

    if palette_file is None:
        inp, palette_file = palette_file, inp

    reader = png.Reader(file=palette_file)
    w, h, rows, info = asRGBorA8(reader)
    channels = info["planes"]
    if not inp:
        rows = list(rows)

    palette_map = make_inverse_palette(rows, channels)

    if inp:
        reader = png.Reader(file=inp)
        w, h, rows, info = asRGBorA8(reader)
        channels = info["planes"]

    # Default for colours not in palette is to use last entry.
    last = len(palette_map) - 1

    def map_pixel(p):
        return palette_map.get(p, last)

    def convert_rows():
        for row in rows:
            yield [map_pixel(p) for p in png.group(row, channels)]

    # Make a palette by sorting the pixels according to their index.
    palette = sorted(palette_map.keys(), key=palette_map.get)
    pal_info = dict(size=info["size"], palette=palette)

    w = png.Writer(**pal_info)
    w.write(out, convert_rows())


def asRGBorA8(reader):
    """
    Return (width, height, rows, info) converting to RGB,
    or RGBA if original has an alpha channel.
    """
    _, _, _, info = reader.read()
    if info["alpha"]:
        return reader.asRGBA8()
    else:
        return reader.asRGB8()


def main(argv=None):
    import sys
    import re

    if argv is None:
        argv = sys.argv

    argv = argv[1:]

    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--palette", type=png.cli_open)
    parser.add_argument(
        "input", nargs="?", default="-", type=png.cli_open, metavar="PNG"
    )

    args = parser.parse_args(argv)

    palette_convert(png.binary_stdout(), args.input, args.palette)


if __name__ == "__main__":
    main()