RE: [libdv-dev] Re: decoding pal dv

[<Mat...@no...>]

Does libdv do all three passes on a 8x8 block? If not this is quite probably
the result of only doing pass1. With three passes I refer to the gathering
of the bits for a 8x8 block that is scattered in other parts of the
macroblock (pass2) and video segment (pass3).

/Mattias

> From: EXT Charles 'Buck' Krasic
>
> I'm fairly certain that the problem you are seeing is a bug in the
> 2-4-8 idct code.  If so, a fix is not yet available.
> 
> I'm going to investigate some tomorrow.  This has been a nagging
> problem for several months that I have not been able to attend to.
> 
> So the short answer is that no fix is currently available.
> 
> One partial workaround: if your camera has a progressive scan mode,
> you should use it.   There should be far fewer 2-4-8 blocks in the
> video.  The 2-4-8 DCT is mainly to deal with motion between fields
> of an interlaced frame.  
> 
> -- Buck
> 
> "Jan M. Hemmi" <jh...@ca...> writes:
> 
> > Dear Charles
> > 
> > I have been using your libdv for decoding dv from a Sony 
> Pal camcorder.
> > While it works generally ok, there are some obvious faults 
> in the image.
> > If one looks closely, the image seems to consist of blocks, 
> that almost,
> > but don't quite match up on the borders. In addition, especially in
> > moving targets, there are often blocks that are very badly 
> out. I tried
> > to look through sourceforge, but could not find any hint, 
> that this was
> > a known problem and has been fixed. 
> > the next lines are the top entry of the change-log file 
> from the version
> > I use, to give you an Idea of the version I use
> > 
> > 2000-04-20  Charles 'Buck' Krasic  <kr...@ac...>
> > * place.c: Fixes to 4:2:0 placement.  Color resembles something
> > like correct now. :}
> > * Add initial macroblock placement for 4:2:0 (IEC61834).  Initial
> > test shows luma is OK, but color isn't working correctly.
> >  
> > I am using libdv though Arne's dvplay.c, after grabbing the 
> images with
> > dvgrab. (without error messages (X)). I normaly only grab every 6th
> > frame, but that does not seem to be responsible for the problem. 
> > Could you tell me of wheter there are any upgrades that 
> might help? I
> > have invested some time in makeing changes both dvplay.c and libdv
> > (minor stuff, such as the order of bytes in the 
> ycrcb_to_rgb24.c ...),
> > to make them better suited to my application (tracking and 
> digitasing of
> > fiddler crab positions), so it would take me quite some 
> time to move to
> > a newer version. However, I would certainly do that if I 
> new it improved
> > the image. The squares do a times pose a problem with my automated
> > tracking. (I know I should have made my changes in a more 
> upgradeable
> > way, but I am a biologist, lacking both skill and time.....
> > 
> > I would greatly appreciate any information.
> > 
> > 
> > thank you
> > 
> > Jan 
> > 
> > 
> > _______________________________________________________
> > 
> > Jan M. Hemmi
> > Visual Sciences
> > Research School of Biological Sciences
> > Australian National University
> > P.O. Box 475
> > Canberra, ACT, 2601
> > 
> > Australia
> > 
> > email: jan...@an...
> > tel  : ++61 (02) 6279 85 61
> > fax  : ++61 (02) 6249 38 08
> > 
> > _______________________________________________________
> 
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