[MPlayer-dev-eng] Re: ccache

[Tobias Diedrich]

Billy Biggs wrote:

> > On Mon, Jan 06, 2003 at 01:00:57AM +0100, Tobias Diedrich wrote:
> > > 
> > > IIRC there was an explanation in an older issue of c't magazine...
> > > Ah, found it (Issue 13/2000, c'tplusrom 1/2000).
> > > 
> > > YUVabc
> > > 
> > > For a samples of Y b samples of UV in odd lines and c samples of UV in
> > > even lines.
> 
>   I don't really think this is valid, since depending on your standard
> for 4:2:0 the chroma samples are located in different places.  Sometimes
> the chroma samples are from the middle of the four Y' samples, sometimes
> it's between the two left samples.

Huh? Why should the be in different places according to the above ?
Anyway I found another definition in an older issue, that seems to match
the Poynton definition better:

c't 20/1999, Page 204ff:

|What does 4:2:2 mean?
|
|Because the Eye can not resolve color differences as good as brightness
|differences, it is enough to only transmit the brightness information (Y,
|Luminance) with full pixel resolution. Color information, that is the Cb
|and Cr components, can be averaged between multiple pixels.
|The notation 4:x:y specifies this kind of subsampling. For 4 pixels at a
|time 4 luma samples are stored, but only x Cb samples and y Cr samples.
|If x and y differ, they change their role in each line.
|
|If one transfers this notation to the bandwith of analog technology,
|one could describe the maximum quality of PAL television with 4:2:2 and
|of VHS recorders with 2:1:1
|
|If another digit is appended, it specifies the resolution of an
|auxiliary channel. There one could store information on how much the
|background should shine through the pixels (key effect).

Explanatory picture attached.

-- 
Tobias								PGP: 0x9AC7E0BC
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