Mailinglist Archive: radeonhd (365 mails)

[Matthias Hopf <mhopf@xxxxxxx>]

On Mar 04, 09 09:38:58 -0800, Yang Zhao wrote:
> > Yang, I wouldn't change that. AFAIU color subsampling in the normal
> > YCb'Cr' color spaces is defined to be interpolative. If it does look to
> > blurry, there could be a different bug. Also, with nearest-neighbor
> > interpolation at least I always stumble over hard edges at smooth
> > surfaces, especially if they are red.
>
> 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, and it turns out to be a
nightmare. JPEG/JFIF, M-JPEG, H.261, and MPEG-1 define the sampling
points at the center of a 2x2 block, while Rec.601 (don't know the
codecs here) defines 4:2:2 to be situated in the center of even lum
samples, and Mpeg-2 mixes both schemes - best take a look at

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.

> 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.

> In any case, I was purely going by user feedback and comparing results
> to the mplayer software converter: http://yangman.ca/r600_xvtest/

The test image is particular suited for letting nearest neighbor lookup
look better. There are others that are favouring interpolation.

But even in this case I like the filtered one better. In this case it's
personal taste. But for a really good interpolation we need gamma
corrected interpolation. Which makes the filter nonlinear.

Matthias

-- 
Matthias Hopf <mhopf@xxxxxxx>      __        __   __
Maxfeldstr. 5 / 90409 Nuernberg   (_   | |  (_   |__          mat@xxxxxxxxx
Phone +49-911-74053-715           __)  |_|  __)  |__  R & D   www.mshopf.de
-- 
To unsubscribe, e-mail: radeonhd+unsubscribe@xxxxxxxxxxxx
For additional commands, e-mail: radeonhd+help@xxxxxxxxxxxx