[Ffmpeg-devel] Bug in snow revision 1.50 - broken lossless mode
Thu Apr 14 02:05:20 CEST 2005
On Wed, 2005-04-13 at 20:52 +0200, Michael Niedermayer wrote:
> > In that case, it would be nice to make 5/3 the default for lossless. It
> > really doesn't make snow look good to have the default mode (9/7,
> > lossless) look so ugly.
> the default of option A should not depend on option B, its confusing and
> problematic, there should be a check for this and the encoder should die with
> an error if 9/7 is used in lossless mode (patch welcome)
I've been testing reducing the levels of decomposition for lossless mode
(5/3 wavelet) (eliminating dwt/idwt completely would require a little
more hacking) and I've got some interesting results:
temp_speak_up is a 512x384 encode (cartoon).
temp is a 512x384 transcode of a high quality xvid (CG animation).
temp_gummi is a 320x240 transcode of a low quality divx (cartoon).
All are 3 seconds long.
temp1 has 5 decomposition levels.
temp2 has 4 decomposition levels.
temp5 has 1 decomposition level.
This indicates that lossless compression is better without dwt/idwt than
with it. It would also make lossless compression substantially faster to
So I suggest not doing dwt/idwt for lossless mode. We'd even get two
birds with one stone, since the rescaled coefficients wouldn't be
causing any more troubles. Any comments or ideas about this?
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