[vorbis-dev] video codec

[Holger Waechtler]

On Fri, 9 Feb 2001, Marco Al wrote:

> From: "Steve Underwood" <steveu at coppice.org>
> 
> > I have a Bugs Bunny cartoon. Its a bit old and noisy. I put it through a
> > codec that tends to glide over the noise. Those big areas of noisy
> > colour, which should be bland and textureless, have become smoother. The
> > result might actually look better than the original. I am happy.
> >
> > Now I come to a natural history film. A close up of a cat with mottled
> > fur. Its a moving, and the picture is a mass of rapidly changing detail
> > - a lot like noise. The codec suppresses it. Now I'm not so happy.
> 
> Thats not the point, its the user's responsibility to present the image as he
> would like them compressed. Suggesting using a noise polluted source to test is
> doing things backwards... if it removes them its ok and if it doesnt remove them
> its still ok, well that was a usefull test. Test with an image sequency which
> naturally has high frequency components.

Noisy high frequency components are a real problem (and will be for any
comprssion codec); they generate lots of uncorrelated coefficients, which
are hard to compress. Perhaps we can get out of this by using a 'texture
syntesizer': analyze some typical frequency characterisics of the
(untransmitted) noise and resynthesize this by adding shaped random noise
to the coefficients on the receiver side. The simplest way would be to
save a single noiselevel-per-scale value.

There were some papers about texture syntesizers available on the web a
while ago, but I don't remember where I've seen them. Check out your
favourite search engine ...

- Holger

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