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Random PNG generator
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#!/usr/bin/env python | |
# Random 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 = "r.png" # Do I really need to explain this? | |
BLOCK_W, BLOCK_H = 8, 8 # block size [pixels] | |
IMAGE_W, IMAGE_H = 240, 135 # image size [blocks] | |
DEPTH = 24 | |
# Color depth [bytes/pixel] | |
# 1 Black and White | |
# 8 Grayscale | |
# 24 RGB | |
# 32 RGBA | |
# Script | |
from os import urandom | |
import struct | |
import zlib | |
def B(x): | |
return struct.pack(">B", x & 0xFF) | |
def I4(x): | |
return struct.pack(">I", x & 0xFFFFFFFF) | |
zero16KiB = b"\0" * 16383 | |
class CompressedPixelWriter: | |
compressor = zlib.compressobj(9) # max compression | |
out = lambda: None | |
length = 0 | |
crc32 = 0x35AF061E # crc32("IDAT") | |
def __init__(self, out): | |
self.out = out | |
def writeRaw(self, b): | |
self.out(b) | |
self.length += len(b) | |
self.crc32 = zlib.crc32(b, self.crc32) | |
def write(self, b): | |
self.writeRaw(self.compressor.compress(b)) | |
# improved write() for many zero bytes | |
def writez(self, num): | |
for i in range(num >> 14): | |
self.out(self.compressor.compress(zero16KiB)) | |
self.crc32 = zlib.crc32(zero16KiB, self.crc32) | |
num &= 0x3FFF | |
self.out(self.compressor.compress(b"\0" * num)) | |
self.crc32 = zlib.crc32(b"\0" * num, self.crc32) | |
self.length += num | |
def writePixels(self): | |
# Empty image data | |
pass | |
def finalize(self): | |
self.writePixels() | |
self.writeRaw(self.compressor.flush()) | |
def rPNG(): | |
global BLOCK_W | |
width = IMAGE_W * BLOCK_W | |
height = IMAGE_H * BLOCK_H | |
bitdepth = 8 # [bit/sample] | |
if DEPTH == 1: | |
bitdepth = 1 | |
if BLOCK_W > 1: | |
raise NotImplementedError("For bit depth of 1, only blocks of width 1 are supported") | |
colortype = 0 | |
elif DEPTH == 8: | |
colortype = 0 | |
elif DEPTH == 24: | |
colortype = 2 | |
elif DEPTH == 32: | |
colortype = 6 | |
else: | |
raise NotImplementedError("Unsupported color depth {0}".format(DEPTH)) | |
compresstype = 0 # zlib (only supported method) | |
filtermethod = 0 # adaptive (only supported method) | |
interlaced = 0 # no | |
maxEntropyBits = DEPTH * IMAGE_W * IMAGE_H | |
print("Projected (maximum) entropy: {0} bits ({1} bytes)".format( | |
maxEntropyBits, | |
(maxEntropyBits + 7) >> 3, | |
)) | |
approxFileSize = (DEPTH * (IMAGE_W + 1) * IMAGE_H * BLOCK_W * BLOCK_H) >> 10 # approx / 1032 | |
approxFileSize += 64 # FIXME | |
approxFileSize += maxEntropyBits | |
print("Estimated file size: {0} bits ({1} bytes)".format( | |
approxFileSize, | |
(approxFileSize + 7) >> 3, | |
)) | |
if DEPTH == 1: | |
bytesPerRow = (DEPTH * IMAGE_W + 7) >> 3 | |
else: | |
bytesPerPixel = DEPTH >> 3 | |
if BLOCK_W > 1: | |
pixelPadding = bytesPerPixel * (BLOCK_W - 1) | |
bytesPerRow = bytesPerPixel * IMAGE_W | |
rowPadding = bytesPerRow * BLOCK_W | |
class RandomPixelWriter(CompressedPixelWriter): | |
def writePixels(self): | |
# This method uses globals, which is probably bad... | |
for y in range(IMAGE_H): | |
# Write scanline | |
if BLOCK_W > 1: | |
self.write(b"\x01") # Sub | |
#prev = bytearray(bytesPerPixel) | |
for x in range(IMAGE_W): | |
# There is no need to subtract from prev, | |
# because random differences are still random. | |
self.write(urandom(bytesPerPixel)) | |
self.writez(pixelPadding) | |
else: | |
self.write(b"\x00") # no PNG filter | |
self.write(urandom(bytesPerRow)) | |
# Repeat previous scanline, at least one time, if needed | |
for i in range(1, BLOCK_H): | |
self.write(b"\x02") # Up filter | |
self.writez(rowPadding) | |
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)) # 13 | |
f.write(IHDR) | |
f.write(I4(zlib.crc32(IHDR))) | |
# IDAT | |
IDAT_len_offset = f.tell() # 33 | |
f.write(b"\0\0\0\0IDAT") | |
pWriter = RandomPixelWriter(f.write) | |
pWriter.finalize() | |
f.write(I4(pWriter.crc32)) | |
# Fix length | |
f.seek(IDAT_len_offset) | |
f.write(I4(pWriter.length)) | |
f.seek(0, 2) # to end | |
# IEND | |
# 0x00000000 + "IEND" + CRC32("IEND") | |
f.write(b"\0\0\0\0IEND\xae\x42\x60\x82") | |
if __name__ == '__main__': | |
rPNG() |
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