/usr/lib/python2.7/dist-packages/pyavm/png.py is in python-pyavm 0.9.2-3.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 | # Pure-python PNG parser
# Copyright (c) 2013 Thomas P. Robitaille
from __future__ import print_function, division
import struct
PNG_SIGNATURE = b'\x89\x50\x4e\x47\x0d\x0a\x1a\x0a'
def is_png(filename):
with open(filename, 'rb') as f:
return f.read(8) == b'\x89\x50\x4e\x47\x0d\x0a\x1a\x0a'
class PNGChunk(object):
@classmethod
def read(cls, fileobj):
self = cls()
# Read in chunk length
length = struct.unpack('>I', fileobj.read(4))[0]
# Read in chunk type
self.type = fileobj.read(4)
# Read in data
self.data = fileobj.read(length)
# Read in CRC
crc = struct.unpack('>I', fileobj.read(4))[0]
# Check that the CRC matches the actual one
if crc != self.crc:
raise ValueError("CRC ({0}) does not match advertised ({1})".format(self.crc, crc))
if length != self.length:
raise ValueError("Dynamic length ({0}) does not match original length ({1})".format(self.length, length))
return self
def write(self, fileobj):
# Write length
fileobj.write(struct.pack('>I', self.length))
# Write type
fileobj.write(self.type)
# Write data
fileobj.write(self.data)
# Write CRC
fileobj.write(struct.pack('>I', self.crc))
@property
def crc(self):
# Note from Python docs: "To generate the same numeric value across all
# Python versions and platforms use crc32(data) & 0xffffffff. If you
# are only using the checksum in packed binary format this is not
# necessary as the return value is the correct 32bit binary
# representation regardless of sign."
# This is indeed true, I see different values in Python 2 and 3.
from zlib import crc32
return crc32(self.type + self.data) & 0xffffffff
@property
def length(self):
return len(self.data)
class PNGFile(object):
@classmethod
def read(cls, filename):
fileobj = open(filename, 'rb')
self = cls()
# Read signature
sig = fileobj.read(8)
if sig != PNG_SIGNATURE:
raise ValueError("Signature ({0}) does match expected ({1})".format(sig, PNG_SIGNATURE))
self.chunks = []
while True:
chunk = PNGChunk.read(fileobj)
self.chunks.append(chunk)
if chunk.type == b'IEND':
break
fileobj.close()
return self
def write(self, filename):
fileobj = open(filename, 'wb')
fileobj.write(PNG_SIGNATURE)
for chunk in self.chunks:
chunk.write(fileobj)
fileobj.close()
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