TIP
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Source that helped me.
NOTE
89 50 4E 47 0D 0A 1A 0A.PNG signature (Check other sigs here)
IHDR chuck follows after signature with no padding inbetween
00 00 00 0D : IHDR chunk length(4 bytes) | IHDR length always fixed for PNG - 13 bytes!
49 48 44 52 : IHDR chunk type(Identifies chunk type to be IHDR)
00 00 05 90 : Image width in pixels(variable 4) | 1424 pixels
00 00 01 11 : Image height in pixels(variable 4) | 273 pixels
08 : Bit depth (1 byte)
06 : Color type (1 byte)
00 : Compression method (1 byte)
00 : Filter method (1 byte)
00 : Interlace method (1 byte)
E5 8A 82 33 : CRC checksum (4 bytes)
Detailed PNG Specification found here.
PNG uses CRC-32
To calculate CRC-32, we need to take ONLY:
----- length NOT INCLUDED
49 48 44 52 (IHDR - chunk type)
00 00 05 90 (width)
00 00 01 11 (height)
08 (bit depth)
06 (color type)
00 (compression)
00 (filter)
00 (interlace)
the whole IHDR EXCEPT length (first 4 bytes): 4948445200000590000001110806000000 ⇒ CRC input
CRC32/ISO-HDLC: E58A8233 Good online tool: CRC Calculator Online