On Fri, 19 Jan 2007 16:38:01 +0100
"Nicolas Boulay" <[EMAIL PROTECTED]> wrote:
> I don't know the status of Yuv texture inside ogp, that could be used
> to reduice bandwith and/or produice a good quality output for video.
Actualy it's not YUV that saves us bandwidth, but subsampling.
YUV just enables us to do subsampling without much los.
> I play a bit with pwc the linux drivers for phillips webcam. They clam
> to deliver yuv 4:2:0 planar. But it's quite hard to find the good
> matrix parameter. the fourcc website give some of them.
There are 2 or 3 widely used parameters for these conversions.
IIRC the most widely used are the ones from CCITT (ITU) and
from the MPEG consortium.
For further reference in the field of video (de)coding, please
have a look at the thread i started a few months ago, about
subsampling/upsampling (sorry, i'm too lazy to look up the subject atm).
There i quoted Michael Niedermayer on some recomendations on what to
use for OGP. You might also want to read the according thread on
ffmpeg-devel.
> I don't know if the mess is the same for all different video capture
> format. But yuv conversion seems not standard at all.
It is standard... a multitude of standards :-)
As Timothy already said, for OGP it is of no matter whether the
the colour values are in YUV or RGB. There will be a conversion
to RGB at some point which can be easily pipelined and thus does
not impose any speed los. The real problem with YUV comes from the
subsampling impossed. Ie for the up sampling we need to perform
some form of interpolation and filtering on the image in either only
vertical direction (4:2:2 -> 4:4:4) or both horizontal and vertical
(4:2:0 -> 4:4:4). And also the UV samples may be half a pixel off
from the Y samples, depending on the used video codec.
Attila Kinali
--
Praised are the Fountains of Shelieth, the silver harp of the waters,
But blest in my name forever this stream that stanched my thirst!
-- Deed of Morred
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