Re: NTSC output from iR.
Moshe Nissim (orad_u++at++netvision.net.il)
Wed, 29 Jan 1997 21:53:43 -0800
Steve Baker wrote:
>
> I said:
>
> > Anybody out there playing with the NTSC encoder on Inf.Reality?
> >
> > I'm trying to videotape some of my normal 1280x1024/60Hz simulations.
> >
> > When I set up ircombine on my iR box for 1280x1024 (60Hz) on one
> > DG-2 output and NTSC on the other, I see an occasional horizontal
> > discontinuity creeping up the NTSC display - no such artifact
> > appears on the regular display.
>
> Well, I think I now understand the problem fully (thanks to some help from an
> old friend at Philips Research)...
>
> NTSC *isn't* 60Hz - it's 59.96Hz, however, your normal SGI CRT
> *is* exactly 60.00000000Hz. Hence, the buffer swap signal in the simulation
> switches the double buffers at 60Hz - which is not in sync with the
> NTSC vertical retrace - so you get a buffer swap partway down the screen.
>
True but,
I think the DG4 absolutely requires that all channels run at the same
swap rate.
So don't beleive everything ircombine says about frequencies...
Anyway, you can "slave" channel 1 to channel 0, wouldn't that guarantee
it will
see the exact pixel-stream as channel 0 ( the CRT )?
Moshe Nissim
Orad Hi-Tec Systems
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