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import struct
import zlib
def encode(buf, width, height):
""" buf: must be bytes or a bytearray in py3, a regular string in py2. formatted RGBRGB... """
assert (width * height * 3 == len(buf))
bpp = 3
def raw_data():
# reverse the vertical line order and add null bytes at the start
row_bytes = width * bpp
for row_start in range((height - 1) * width * bpp, -1, -row_bytes):
yield b'\x00'
yield buf[row_start:row_start + row_bytes]
def chunk(tag, data):
return [
struct.pack("!I", len(data)),
tag,
data,
struct.pack("!I", 0xFFFFFFFF & zlib.crc32(data, zlib.crc32(tag)))
]
SIGNATURE = b'\x89PNG\r\n\x1a\n'
COLOR_TYPE_RGB = 2
COLOR_TYPE_RGBA = 6
bit_depth = 8
return b''.join(
[SIGNATURE] +
chunk(b'IHDR', struct.pack("!2I5B", width, height, bit_depth, COLOR_TYPE_RGB, 0, 0, 0)) +
chunk(b'IDAT', zlib.compress(b''.join(raw_data()), 9)) +
chunk(b'IEND', b'')
)
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