[Linux-fbdev-devel] Re: fbdev, console, (video) overlay/underlay& fbtv

[Geert U. <ge...@li...>]

On Wed, 11 Jul 2001, Romain Dolbeau wrote:
> Geert Uytterhoeven wrote:
> > Not to mention separation of even/odd scanlines and luminance/chrominance on
> > some chipsets.

On some chipsets you have not one buffer containing all pixel data, but two
buffers: one for the even scanlines, and one for the odd scanlines.

It's also possible that the luminance and chrominance data are separated.
For YUV 4:2:2 (i.e. one Y value for each pixel, but only one U and one V for
each two pixels: YUYV), that means
  - one buffer for the Y data for the even scanlines
  - one buffer for the Y data for the odd scanlines
  - one buffer for the UV data for the even scanlines
  - one buffer for the UV data for the odd scanlines

I don't know whether this is done in any PC chipset, but it happens in chipsets
for set-top boxes.

> > Or better: a chroma key range ([YUV]{min,max}). Some hardware supports that.
> 
> Could you elaborate on those 2 ? I haven't seen that yet (not
> surprising,
> I'm for from an expert on the subject :-)

    pixel_is_transparent if (Ymin <= Y <= Ymax) && (Umin <= U <= Umax) &&
			    (Vmin <= V <= Vmax)

compare this to the single chroma key value:

    pixel_is_transparent if Y == Ykey && U == Ukey && V == Vkey

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@li...

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds