Re: JPEG file internal structure

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#2115

From: Marco Schmidt
Date: Tue, 04 Sep 2007 08:03

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fup2 r.p.d; best group is probably comp.compression, though

kbhat@kaxy.com:

>> I am looking for some information on the internal structure of a JPEG
>> file.  I was playing with a handful of bits in a JPEG file as part of
>> a steganagraphy experiment and I saw something remarkable.  I am able
>> to cause a lateral shifting in the file.  It is as if someone has torn
>> the right quarter of the picture and pasted it on the extreme left.  I
>> was certainly expecting loss of clarity in the picture, but seeing
>> such a remarkable phenomenon has left me completely dumbstruck.  Any
>> suggestions what might be causing this?

If part of the bitstream is corrupted, the decoder takes up decoding
at the next restart marker or wherever the bitstream makes sense to it
again. Decoding resumes at an incorrect position because the decoder
does not know how many pixels (MCUs) it skipped over. Hence,
everything is shifted.

Regards,
Marco

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From: Marco Schmidt <marcoschmidt@geocities.com>
Newsgroups: comp.os.ms-windows.programmer.win32,comp.sources.d,rec.photo.digital,adobe.photoshop.windows,comp.graphics.algorithms
Subject: Re: JPEG file internal structure
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Date: Tue, 04 Sep 2007 10:03:24 +0200
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