jm + image-compression   1

Xerox scanners/photocopiers randomly alter numbers in scanned documents · D. Kriesel
Pretty major Xerox fail: photocopied/scanned docs are found to have replaced the digit '6' with '8', due to a poor choice of compression techniques:
Several mails I got suggest that the xerox machines use JBIG2 for compression. This algorithm creates a dictionary of image patches it finds “similar”. Those patches then get reused instead of the original image data, as long as the error generated by them is not “too high”. Makes sense. This also would explain, why the error occurs when scanning letters or numbers in low resolution (still readable, though). In this case, the letter size is close to the patch size of JBIG2, and whole “similar” letters or even letter blocks get replaced by each other.
jbig2  compression  xerox  photocopying  scanning  documents  fonts  arial  image-compression  images 
august 2013 by jm

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