[Ffmpeg-devel] Bug in snow revision 1.50 - broken lossless mode

[Yartrebo]

On Wed, 2005-04-13 at 15:26 -0400, D Richard Felker III wrote:
> On Wed, Apr 13, 2005 at 12:13:53PM +0200, Michael Niedermayer wrote:
> > Hi
> > 
> > On Wednesday 13 April 2005 06:03, Yartrebo wrote:
> > > Michael, those rescaled IDWT coefficients (revision 1.50) appear to have
> > > broken lossless mode quite bad. It's all fuzzy now and is similar in
> > > quality to quant=10 or 20. It happens for all inputs I've tried.
> > 
> > the regression tests worked yesterday and they do test lossless with the 5/3 
> > wavelet
> > the 9/7 wavelet is with the scaling merged not bijective with fixed point 
> > numbers, its bijective if rational or real numbers are used, but as the 5/3 
> > wavelet is superior for lossless (at least it was in my tests) thats really 
> > irrelevant
> > but then again, dont hesitate to look at the lifting steps for the 9/7 
> > wavelet, maybe you can come up with a better solution so that this 
> > dissadvantage can be avoided
> 
> is the problem just that we have too few bits? because fracbits count
> certainly be increased... i.e. we never seem to use more than 24 bits
> or so out of the 32...
> 
> rich
We currently use up to 26 bits (+/- 2^24 is the range of values
determined empirically) ... I'll give it a spin with higher fracbits and
report my findings.