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
111
112
113
| import sys
import struct
import binascii
class PNG:
def __init__(self, binary):
self.binary = binary
def is_PNG(self):
return struct.unpack_from(">Q", self.binary, 0)[0] == 9894494448401390090
def chunk(self, offset):
chunk = struct.unpack_from(">I4s", self.binary, offset)
chunk += struct.unpack_from(">I", self.binary, offset + chunk[0] + 8)
return chunk
def chunk_data(self, chunk, offset):
if chunk[1] == b'IHDR':
return self.IHDR(chunk, offset)
elif chunk[1] == b'sRGB':
return self.sRGB(chunk, offset)
elif chunk[1] == b'gAMA':
return self.gAMA(chunk, offset)
elif chunk[1] == b'pHYs':
return self.pHYs(chunk, offset)
elif chunk[1] == b'tEXt':
return self.tEXt(chunk, offset)
elif chunk[1] == b'tIME':
return self.tIME(chunk, offset)
elif chunk[1] == b'IDAT':
return self.IDAT(chunk, offset)
elif chunk[1] == b'IEND':
return self.IEND(chunk, offset)
else:
return False
def CRC32(self, chunk, offset):
crc_data = chunk[1]
crc_data += struct.unpack_from(">%ds" % chunk[0], self.binary, offset + 8)[0]
return binascii.crc32(crc_data)
def IHDR(self, chunk, offset):
labels = ('width', 'height', 'bit depth', 'colour type', 'compression method', 'filter method', 'interlace method')
values = struct.unpack_from(">2I5B", self.binary, offset + 8)
return dict(zip(labels, values))
def sRGB(self, chunk, offset):
labels = ('rendering intent',)
values = struct.unpack_from(">B", self.binary, offset + 8)
return dict(zip(labels, values))
def gAMA(self, chunk, offset):
labels = ('image gamma',)
values = struct.unpack_from(">I", self.binary, offset + 8)
return dict(zip(labels, values))
def pHYs(self, chunk, offset):
labels = ('pixels per unit, X axis', 'pixels per unit, Y axis', 'unit specifier')
values = struct.unpack_from(">IIB", self.binary, offset + 8)
return dict(zip(labels, values))
def tEXt(self, chunk, offset):
offset += 8
data_offset = 0
keyword = ''
while(True):
c = struct.unpack_from(">s", self.binary, offset + data_offset)
if c[0] == b'\x00': break
keyword += str(c[0])
data_offset += 1
data_offset += 1
text_string = ''
while(data_offset < chunk[0]):
c = struct.unpack_from(">s", self.binary, offset + data_offset)
text_string += str(c[0])
data_offset += 1
return {'keyword': keyword, 'text string': text_string}
def tIME(self, chunk, offset):
labels = ('year', 'month', 'day', 'hour', 'minute', 'second')
values = struct.unpack_from(">H5B", self.binary, offset + 8)
return dict(zip(labels, values))
def IDAT(self, chunk, offset):
labels = ('image data',)
values = ('TODO',)
return dict(zip(labels, values))
def IEND(self, chunk, offset):
return ()
with open('./sunrise.png', 'rb') as f:
png = PNG(f.read())
if not png.is_PNG():
print('ERROR: This is not png')
sys.exit(1)
offset = 8
while(True):
print('--------------------')
chunk = png.chunk(offset)
print(chunk)
if(chunk[1] == b'IEND'):
break
chunk_data = png.chunk_data(chunk, offset)
print(chunk_data)
crc = png.CRC32(chunk, offset)
if chunk[2] != crc:
print('WARNING: CRC error. expected: %d actual: %d' % (chunk[2], crc))
if chunk_data == False:
break
offset += chunk[0] + 12
|
