[libdv-dev] Re: decoding pal dv

[Charles 'B. K. <kr...@cs...>]

Jan,

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
> 
> _______________________________________________________