[MPlayer-dev-eng] [LONG] PSNR comparison, new source and results

[Michael Niedermayer]

Hi

On Wednesday 16 June 2004 15:53, Jan Knutar wrote:
> On Wednesday 16 June 2004 12:18, Romain Dolbeau wrote:
> > Jan Knutar wrote:
> >
> > qpel not only raise the execution time by over 63% on
> > average, it also decrease the PSNR in all case. trell
> > isn't anywhere as expensive, and it does give you a
> > nice improvement all the time. *dia=-2 is a tiny bit
> > better and not much more expensive tha *dia=1.
>
> I did a comparison of qpel at different bitrates, with very basic
> options. Source material is the trailer for "Kate & Leopold", from the
> PAL DVD. It's full screen 4:3, and I encode it unscaled.
>
> I used mbd=2:v4mv, 2 pass encoding with different bitrates, with and
> without qpel.
>
> The findings:
>
> bitrate < ~750:	qpel decreases psnr
> ~ 750 < bitrate < 2000:	qpel increases psnr
> 2000 < bitrate:	qpel decreases psnr
>
> Perhaps more interesting is the same expressed in bits per pixel instead
> of bitrate, like this:
>
> bpp < ~ 0.075		qpel decreases psnr
> ~ 0.075 < bpp < .20	qpel increases psnr
> .20 < qpel	qpel decreases psnr
>
>
> What surprised me was that qpel at high bitrates actually decrease PSNR.
one possible explanation is that at a bitrate similar to the source bitrate we 
are really trying to store the mpeg2 compression artefacts and mpeg4-hpel is 
better then mpeg4-qpel at storing mpeg2-hpel
it would be interresting to see if the psnr decrease at high bitrates exists 
for uncompressed sources too ...

[...]
-- 
Michael
level[i]= get_vlc(); i+=get_vlc();		(violates patent EP0266049)
median(mv[y-1][x], mv[y][x-1], mv[y+1][x+1]);	(violates patent #5,905,535)
buf[i]= qp - buf[i-1];				(violates patent #?)
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