[XviD-devel] XviD waterkmark?

Michael Militzer michael at xvid.org
Sun Jul 10 20:17:06 CEST 2005


Hi,

you should check how your modifications influence the picture quality (e.g.
by measuring achieved PSNR values of the modified vs. unmodified encoder).
If you mess around with the transform coefficients to add the watermark, 
this may introduce a mismatch with unmodified decoders, which will 
accumulate (and become visible). So you should take this into account...

Michael


Quoting Jakub Piotrowski <jpp at poczta.onet.pl>:

> Hi,
> 
> In general idea of watermarking is that they do not interfere with the
> standard - its only modification of payload. In my case, it is changing least
> significant bits of macroblocks - this results in probably slight (not yet
> tested:)) changes to the film. So I'm not changing bitstream sythax (this
> would be useless), I'm only messing with bits vaules.Changes are based on
> selected bits xor function (determined by a random number, which acts like an
> encryption-key).
> 
> Benefits are: You get extra data channel without incrasing bitrate, and (not
> yet but maybe in future) You get robust marking tool. Of course robustness
> can ba achieved only by increasing number of bits that are involved in
> marking process, and to avoid lowering visual quality it would require some
> kind of visual-adapting algorithm to be implemented (just like phillips did
> for JAWS), but this is good direction, and I'll try this way - after I
> complete first stage.
> 
> And of course main target is not to include subtitlest. It is supposed to
> become a fingerprinting/authentication system. For now, it may act as a part
> of broadcast control system - but this can also be done with media containers
> (btw. there are also a few projected watermarks for media containers as well,
> e.g. for xmt scene structure in mpeg-4).
> 
> Jakub
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