ASCII Hex Filter
From GNUpdf
PDF Reference 3.3.1 ASCIIHexDecode Filter:
The ASCIIHexDecode filter decodes data that has been encoded in ASCII hexadecimal form. ASCII hexadecimal encoding and ASCII base-85 encoding convert binary data, such as image data, to 7-bit ASCII characters. In general, ASCII base-85 encoding is preferred to ASCII hexadecimal encoding because it is more compact: it expands the dat by a factor of 4:5, compared with 1:2 for ascii hexadecimal encoding. The ASCIIHexDecode filter produces one byte of binary data for each pair of ASCII hexadecimal digits (0-9 and A-F or a-f). All white-space characters are ignored. A right angle bracket character (<) indicates EOD. Any other characters cause an error. If the filter encounters the EOD marker after reading an odd-number of hexadecimal digits, it behaves as if a 0 followed the last digit.
