Re: [XviD-devel] XviD-1.1-Beta 1 bugs summary

[Michael Militzer <michael@xxxxxxxx>]

Hi,

thanks for the links. One thing's for sure: cartoon mode is not intended
to be used for coding natural images. This will produce artifacts and I
wouldn't consider this a bug. Regarding the artifacts in cartoon-like images,
it looks as if MBs are skipped that actually shouldn't have been skipped
(because they're moving). It seems this effect is amplified by either 
adaptive quantization or b-frames (or both). 

Cartoon mode is rather aggressively forcing skip mode because cartoons have
a lot of stationary motion. Wrong skip decisions cause artifacts. I'll try
to think of something, which eliminates these wrong decisions without
harming the compression efficiency...

bye,
Michael


Quoting nvidiadx@xxxxxxxxxxxx:

> 
> 
> On Wed, 23 Feb 2005 23:49:30 -0800 Dirk Knop <dknop@xxxxxxxxx
> goettingen.de> wrote:
> >Aloha!
> >
> >Michael Militzer wrote:
> >
> >>Hi,
> >>
> >>Quoting Dirk Knop <dknop@xxxxxxxxxxxxxxxxxxxxxx>:
> >>
> >>  
> >>
> >>>- GMC has a bug. With very much motion, some blocks get totally 
> >>>displaced. The issue is the same no matter if decoded with 
> >libavcodec or 
> >>>xvid.
> >>>    
> >>>
> >>
> >>Do you have a sample demonstrating this effect? Either the coded 
> >(wrong)
> >>bitstream or a source file + settings to reproduce the problem?
> >>  
> >>
> >
> >Someone reporting this bug at doom9 posted an archive here: 
> >http://s2.yousendit.com/d.aspx?id=1IRU00JPFMEFR26USGL9OUJOF1
> >
> >Don't know if it's still online, but it contains the source, the 
> >avs 
> >script and some broken encodes ;)
> >
> >>>- Some issue with cartoon mode and bvhq (well, cruncher may 
> >report it 
> >>>better :) ): some white blocks sometimes floating around within 
> >high motion.
> >>>    
> >>>
> >>
> >>Is this really _only_ happening with bvhq? Iirc, the cartoon mode 
> >doesn't add
> >>any special optimizations for b-frames - in fact, it wasn't even 
> >meant for
> >>using it with b-frames (at least I didn't test it much). Do you 
> >have a sample
> >>clip for this problem? I suspect that probably some MBs are 
> >skipped in 
> >>b-frames, which shouldn't have been skipped - but you know, 
> >cartoon mode
> >>rather aggressively forces the use of skip mode...
> >>  
> >>
> >This is a cruncher-report, he says he can always reproduce it. 
> >Will ask 
> >him to report more on it.
> >
> >Regards
> >Koepi
> 
> Yes my initial thought was b-vop is couseing this behaviour in use 
> with cartoon mode but that assumption was wrong it is cartoon mode 
> + adaptive quantization thats couseing it, other reports and 
> samples showing that problem can be found @ the following places
> 
> http://forum.doom9.org/showthread.php?s=&threadid=90596
> http://forum.doom9.org/showthread.php?s=&threadid=88367
> http://cruncher.mufflastig.com/XviD/cartoonbug/
> 
> SCNR
> CruNcher
> 
> 
> 
> 
> 
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