[XviD-devel] Qeustion about encoding rgba images.

MAILER-DAEMON MAILER-DAEMON
Wed May 11 16:52:23 CEST 2005


Thanks for the clarification.

That's what I thought from looking at the src code but wanted to
make sure before I implemented the alpha channel support. I don't
know if what I come up with will be good enough to commit but I will
be glad to if that is the case.

Also as mentioned in the previous post when I decode the encoded streams
with the XVID_CSP_RGBA it returns it in XVID_CSP_BGA format (I just 
verifyed it). I would think this is a bug but maybe not?


On Wed, 11 May 2005, Michael Militzer wrote:

> Hi,
> 
> right, the MPEG-4 standard allows coding of alpha channels - however not in
> all profiles. XviD just supports the MPEG-4 simple and advanced simple 
> profiles and does _not_ support proper coding of alpha channels.
> 
> You can use input images with a alpha channel (e.g. XVID_CSP_RGBA) but upon
> conversion into YV12, XviD's internal colorspace, the alpha channel will be
> _omitted_ by XviD. Therefore, the alpha plane also cannot be reconstructed
> anymore at the decoder side then...
> 
> If you really need alpha channels, you could either try adding support for
> them to XviD yourself or you could have a look at the MPEG-4 reference soft-
> ware (since I'm not aware of any popular MPEG-4 encoder implementation
> offering support for proper alpha channel coding).
> 
> bye,
> Michael
> 
> 
> Quoting MAILER-DAEMON at edu.bnhof.de:
> 
> > 
> > I noticed that for encoding/decoding color space there were
> > XVID_CSP_RGBA. But when I use that option the encoded mpeg
> > stream seems to be identical to XVID_CSP_BGR. If I want to
> > decoded in RGB space will it always be interleaved BGR?
> > 
> > Also looking further into the code in image.h it seems image struct does 
> > not have an alpha channel. Is there a different way of specifying the 
> > alpha channel to encode? If I remember correctly MPEG-4 has allows alpha
> > channels. If its possibel can anyone point me to where I might 
> > look?
> > 
> > I'd appreciate any help.
> > _______________________________________________
> > XviD-devel mailing list
> > XviD-devel at xvid.org
> > http://list.xvid.org/mailman/listinfo/xvid-devel
> > 
> 
> 
> 
> 
> 

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