On Tue, 5 Feb 2002, Steve Kirkendall wrote:
> Billy Biggs wrote:
> >
> > Mark Vojkovich ([EMAIL PROTECTED]):
>
> Thanks, both of you, for your comments. My server still dies, but I'm
> feeling a little more confident now.
>
> > > On Mon, 4 Feb 2002, Steve Kirkendall wrote:
> > >
> > > I'd be surprised if a voodoo card could do 2048x2048. It's one of the
> > > worst overlay hardware. Doesn't seem to do the correct YUV->RGB
> > > colorspace conversion either (ie. not CCIR601).
> >
> > Arguably we shouldn't be using the 601 transfer functions anyway, we
> > should use the ITU-R BT.709 ones instead since CRTs are likely closer to
> > the HDTV standard. I'd also add that MPEG2 video actually specifies the
> > 709 transfer function (those mmx'ified yuv2rgb routines everywhere are
> > usually doing the outdated transfer).
> >
> > Do you know what conversion they are using?
>
> I tried both, and 709 looks a lot better than 601. My XMMS plugin
> starts with an RGB image intended for a window, and converts it to a
> YUV image just so I can use the XVideo scaling hardware. I can toggle
> between windowed RGB and full-screen YUV with a single keystroke, so
> color differences are easy to spot. 601 conversion resulted in an
> objectionable amount of color drift. 709 still has some trouble with
> shades of magenta, but other than that it looks very good.
That's because the 3dfx hardware isn't doing 601 like everybody
else. There might be a way to fake it with their secondary palette.
The Voodoo has a second palette one can use for the overlay. But
I haven't looked into the math to see if it works out right.
>
> So... Do you think this is just a quirk of the Voodoo3 card? If 601
> would look better on other cards, then it might be worthwhile to add
> an option for selecting the conversion formula. Or does XVideo have
> some flag tucked in the XvFormatInfo struct to indicate the conversion
> rule, so I can automatically choose the correct conversion?
601 would look better on all other hardware. There's no way to
query it. It was my intention that everyone would use 601, but I didn't
realize that 3dfx was an oddball in this respect.
Mark.
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