[Ffmpeg-devel] upsampling of subsampled video data

[Michael Niedermayer]

Hi

On Sun, Sep 10, 2006 at 10:25:25PM +0200, Attila Kinali wrote:
> On Sun, 10 Sep 2006 12:17:41 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > 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
> 
> Does this mean, that the C samples are inbetween the Y
> samples and thus have to be interpolated in vertical
> direction too before converting to RGB?
> (apart from the missing sample every second line)

as rich already said yes though i suspect that a 1/2 pixel position error
will be less noticeable then not interpolating at all, and of course the
position is just what the spec says, if that really matches the true sample
locations may or may not be the case, depending on the source ...

also even though ive no clue about hw design, somehow i think that a
optional prefilter which shifts the chroma samples by 1/4 pixel could be
helpfull for the complexity of the interpolating stuff



[...]
>  
> > the following codecs depend on 4:1:1 support (or a sw converter to make 4:2:2
> [...]
> > the following codecs depend on 4:1:0 support (or a sw converter to make 4:2:0
> > out of their 4:1:0)
> 
> >From the list of codecs that use these two, i guess that
> these are special cases that can be left out if there is
> not enough space (which there isnt)
> 
> BTW: while we are at it, how important is it to have a
> YUV->RGB converter that supports different standards?
> Ie, IIRC there are 3 different coefficients for YUV<->RGB
> conversion by different standards groups. Is it important
> to have a programmable converter to select one of these,
> or would be one constant enough without too much quality
> los for the others?

my guess would be that a single one will be ok if complexity is an issue and
it sounds like that is the case

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

In the past you could go to a library and read, borrow or copy any book
Today you'd get arrested for mere telling someone where the library is