#!/usr/bin/env python
# Paul Sladen, 2011-12-01
from PIL import PngImagePlugin, Image, ImageFile
#Image.DEBUG = True

# Meh, why doesn't PIL support this already?
def chunk_iTXt(self, pos, len):
    s = ImageFile._safe_read(self.fp, len)
    # http://www.w3.org/TR/PNG/#11iTXt
    k, structure = s.split('\0', 1)
    compression_flag, compression_method = map(ord, structure[:2])
    language_tag, translated, t = structure[2:].split('\0', 2)
    if compression_flag == 0:
        v = t.decode('utf-8')
    elif compression_flag == 1 and compression_method == 0:
        import zlib
        v = zlib.decompress(t).decode('utf-8')
    else:
        raise SyntaxError("Unknown compression request %d in iTXt chunk" %
                          compression_method)
    self.im_info[k] = {'translated_keyword': translated.decode('utf-8'),
                       'language_tag': language_tag,
                       'text': v}
    self.im_text[k] = v
    return s

PngImagePlugin.PngStream.chunk_iTXt = chunk_iTXt

def test(f):
    i = PngImagePlugin.PngImageFile(f)
    print i.info, i.text
    steno = i.text['Comment'].decode('base64')

if __name__ == '__main__':
    test('cyber.png')