Maximum (sized) PNG generator

maxpng.py

#!/usr/bin/env python
# Maximum PNG generator
__copyright__ = "Copyright (C) 2016 Victor Zheng"
__licence__ = "GNU GPL v3"

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# Settings

OUTPUT_FILE = "max.png" # Do I really need to explain this?
IMAGE_W, IMAGE_H = 0x7FFFFFFF, 0x7FFFFFFF # image size [pixels]
DEPTH = 4
# Color depth [bytes/pixel]
#   1 Grayscale
#   3 RGB
#   4 RGBA

# Script
import struct
import zlib

def B(x):
    return struct.pack(">B", x & 0xFF)

def I4(x):
    return struct.pack(">I", x & 0xFFFFFFFF)

pixels = b"" # too lazy...

def writePNG():
    width = IMAGE_W
    height = IMAGE_H
    bitdepth = 16 # [bit/sample]
    if DEPTH == 1:
        colortype = 0
    elif DEPTH == 3:
        colortype = 2
    elif DEPTH == 4:
        colortype = 6
    else:
        raise NotImplementedError("Unsupported color depth " + DEPTH)
    compresstype = 0 # DEFLATE (only supported method)
    filtermethod = 0 # adaptive (only supported method)
    interlaced = 0 # no

    with open(OUTPUT_FILE, "wb") as f:
        # Signature
        f.write(b"\x89PNG\r\n\x1A\n")
        # IHDR
        IHDR = b"IHDR" \
            + I4(width) \
            + I4(height) \
            + B(bitdepth) \
            + B(colortype) \
            + B(compresstype) \
            + B(filtermethod) \
            + B(interlaced)

        f.write(I4(len(IHDR) - 4))
        f.write(IHDR)
        f.write(I4(zlib.crc32(IHDR)))
        # IDAT
        compressor = zlib.compressobj(9) # max compression
        IDAT = b"IDAT" + \
            compressor.compress(pixels) + \
            compressor.flush()
        f.write(I4(len(IDAT) - 4))
        f.write(IDAT)
        f.write(I4(zlib.crc32(IDAT)))
        # IEND
        # 0x00000000 + "IEND" + CRC32("IEND")
        f.write(b"\0\0\0\0IEND\xae\x42\x60\x82")

if __name__ == '__main__':
    writePNG()

z_max.png