Extracting the WH 7535 PDF JPEG

Our friend Hermitian is having troubles finding the ‘YCbCr’ comment tag in the jpeg embedded in the wh-lfbc-scanned-xerox-7535-wc.pdf file. I previously outlined how to do this:

qpdf –show-object=12 –raw-stream-data wh/wh-lfbc-scanned-xerox-7535-wc.pdf >stream12.png

Note that the png extension is used to ‘fool’ wordpress into accepting the document. You can download and save it.

Remember Obj 12?

obj 12 0
 Type: /XObject
 Referencing: 32 0 R
 Contains stream

  <<
    /BitsPerComponent 8
    /ColorSpace /DeviceRGB
    /DecodeParms [null 32 0 R]
    /Filter [/FlateDecode/DCTDecode]
    /Height 1280
    /Length 231258
    /Subtype /Image
    /Type /XObject
    /Width 1664
  >>

This will extract Obj 12 as a raw data stream. If you cannot get qpdf to work, you can use a hex editor to extract Obj 12 stream from the PDF directly.

Deflate the stream using

python ./deflate.py stream12.png stream12.jpg

I will even give you the deflate.py script

import zlib
import sys

args = sys.argv

if len(args) != 3:
	print("Usage python.exe "+args[0]+" ")
	exit(0)

input = args[1]
output = args[2]

file_read = open(input,'rb')
buffer = file_read.read()
decomp = zlib.decompress(buffer)
file_write = open(output,'w')
file_write.write(decomp)

stream12.jpg

jpeginfo -C stream12.jpg

stream12.jpg 1664 x 1280 24bit n/a N 235646 “YCbCr”