[Ffmpeg-devel] upsampling of subsampled video data

[Michael Niedermayer]

Hi

On Sun, Sep 10, 2006 at 10:34:54AM +0200, Attila Kinali wrote:
> Moin,
> 
> On the OGP mailinglist there is currently a discussion going on
> on how and when to perform upsampling of subsampled YUV data.
> 
> My biggest question is whether the U and V data is just
> coppied to all the pixels or is it interpolated between
> the sample points?
> 
> If it's interpolated, how much image quality los would it
> be to just copy it?

well, ideally it should be interpoated, the swscaler currently does for
yuv->yuv interpolation/copying as specified by the user (-sws parameter in 
         mplayer)
yuv->rgb interpolation/copying as specified by the user upto 4:2:2 and
         then horizontally copying U/V once and finally yuv->rgb conversation
         code to do this with full interpolation is half finished in svn since
         years (patch would be welcome ...)

the unscaled 4:2:0 yuv->rgb converter used by us and many other projects
always copies UV around, which does sometimes look worse (well vissible on
diagonal red-<some other color> edges)


> 
> Additionaly, would it be enough to support only 4:2:2 and 4:2:0
> as the most common formats, or shall other "odd" formats like 4:1:1,
> 3:1:1 or 3:1:0 ?

well, lets see, first heres a list of the common formats with ideal sample 
positions shown below too
progressive 4:2:0 (mpeg1)
Y Y Y Y
 C   C
Y Y Y Y

Y Y Y Y
 C   C
Y Y Y Y


progressive 4:2:0 (mpeg2/mpeg4)
Y Y Y Y
C   C
Y Y Y Y

Y Y Y Y
C   C
Y Y Y Y


interlaced 4:2:0 (mpeg2/mpeg4)
field A     field B
Y Y Y Y
C   C
            Y Y Y Y

Y Y Y Y
            C   C
            Y Y Y Y
note, its very important that only luma and chroma samples from the same field
      are used in building rgb values or pretty ugly artifacts appear


4:2:2 (mpeg2/mpeg4/ITU BT601/dv)
@ Y @ Y   (@=Y+C)

@ Y @ Y

@ Y @ Y

@ Y @ Y


4:1:1 (dv)
@ Y Y Y   (@=Y+C)

@ Y Y Y

@ Y Y Y

@ Y Y Y

now which are important? mpeg2/4 4:2:0 progressive and interlaced certainly
are and 4:2:2 too

the following codecs depend on 4:1:1 support (or a sw converter to make 4:2:2
out of their 4:1:1)
Cirrus Logic AccuPak
Creative YUV (CYUV)
Miro VideoXL codec
NTSC DV
from these probably only DV is relevant the others are obscure


the following codecs depend on 4:1:0 support (or a sw converter to make 4:2:0
out of their 4:1:0)
Sorenson Vector Quantizer 1
intel indeo2
intel indeo3
ATI VCR1


and 3:?:? well iam not even sure what they mean but iam sure they are
irrelevant from the yuv->rgb perspective of a grafic card

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or copy any book
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