Mailinglist Archive: radeonhd (365 mails)

[Alex Deucher <alexdeucher@xxxxxxxxx>]

On Thu, Mar 5, 2009 at 12:34 PM, Yang Zhao <yang@xxxxxxxxxx> wrote:
> 2009/3/5 Matthias Hopf <mhopf@xxxxxxx>:
> > On Mar 04, 09 09:38:58 -0800, Yang Zhao wrote:
> > > Does MPEG/BT.601/BT.709 define an upscaling method for chroma when
> > > decoding, or is that up to each decoder implement as they see fit? I
> >
> > It seems that even the definition of where the subsamples lie is exactly
> > defined, and different per codec...
> >
> > http://books.google.com/books?id=ra1lcAwgvq4C&pg=RA1-PA93&lpg=RA1-PA93&dq=chroma+subsampling+interpolation&source=bl&ots=bOh8AFXU9a&sig=QmssmmY3maRjYrSw27vcAi3OKZA&hl=en&ei=_e2vSbjFAcOe_ga94ri1BA&sa=X&oi=book_result&resnum=3&ct=result#PRA1-PA93,M1
> >
> > I haven't found a spec for how the values have to be reconstructed. But
> > the original sample positions would influence that very much.
>
> From page 93:
> "To interpolate the missing chroma samples prior to conversion back to
> R'G'B', low-end systems simply replicate the subsampled Cb and Cr
> values throughout the 2x2 quad. This technique is ubiquitous in
> JPEG/JFIF... and is used in M-JPEG, H.261, and MPEG-1"
>
> This seems to imply that stored chroma is upscaled using nearest-point
> interpolation by standard, or at least that's the common way for
> renderers to operate. This is the same conclusion I arrived at after
> comments of blurriness prompted me to investigate how the up-sampling
> is done.
>
>
> > > failed to find any secondary source information on this, and acquiring
> > > specs myself is a PITA.
> >
> > Read http://www.glennchan.info/articles/technical/chromata/chromata.html
> >
> > IMHO bilinear filtered already looks *much* better than nearest
> > neighbor.
> >
> > http://www.glennchan.info/articles/technical/chroma/chroma1.htm
> > looks like an interesting read. Haven't read yet, though.
>
> That's one of the more useful sites I did manage to find, but I didn't
> give it much thought since it seemed to be geared toward how to encode
> the stills such that artifacts as a result of nearest-neighbour
> decoding doesn't end up producing crappy results. Looking over it
> again, it seems to have some hints for decoders as well. I'll give it
> a better read through.
>
>
> In any case, I'll keep working on this to see if I can come up with a
> better solution. It's easier to let results do the talking.
>
> I'll check my university's library catalogue to see if it has copies
> of the various MPEG-related specs.

You might also check the hw setup in the intel or nouveau drivers as a
reference for comparison.

Alex
-- 
To unsubscribe, e-mail: radeonhd+unsubscribe@xxxxxxxxxxxx
For additional commands, e-mail: radeonhd+help@xxxxxxxxxxxx