Re: YUV format

On Fri, 27 Dec 2002, Holger Waechtler wrote:

> Holger Waechtler wrote:
> > Dustin Stuart wrote:
> >
> >> YUV12 saves the chrominance planes at 1/4 the resolution of the luminance
> >> plane right? because the eye is less sensitive to colour than shade.
> >>
> >> Instead of reducing the colour resolution, why not simply quantize the
> >> colour information more heavily. This way the encoder could be more
> >> flexible
> >> about how much colour information is kept (hopefully reducing blocky
> >> artifacts in areas where the colour changes abruptly).
> >
> >
> > This is done anyway. Right now the U and V component images get 1/8 and
> > the V component images gets 1/8 of the bit budget.
>    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> sorry, this should read:
>
> ...the Y component image gets 6/8, the U and V component images get 1/8
> each...

For the input mode of ppm files this is fine because you start out with
the same size plane for Y, U and V (after conversion from RGB), but for
YUV420 where the U and V planes are already 1/4 size, is it still
appropriate to do this 6:1:1 reduction, or will that just reduce the color
data even more than the YUV420 format already has?

Ed Okerson

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