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From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.graphics
Subject: Re: Mixing computer and video signals
Message-ID: <22455@sun.uucp>
Date: Tue, 30-Jun-87 20:13:34 EDT
Article-I.D.: sun.22455
Posted: Tue Jun 30 20:13:34 1987
Date-Received: Thu, 2-Jul-87 01:20:09 EDT
References: <173@mv06.ecf.toronto.edu> <3119@eagle.ukc.ac.uk> <804@puff.WISC.EDU> <15342@onfcanim.UUCP>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 35

In article <15342@onfcanim.UUCP> dave@onfcanim.UUCP (Dave Martindale) writes:
.>In article <804@puff.WISC.EDU> upl@puff.WISC.EDU (Future Unix Gurus) writes:
.>>By the way, a good professional studio should be able to genlock itself to
.>>the NTSC out from your computer, thus you could use the studio's chroma
.>>key to build the images you want. Using decent studio equiptment has some
.>>real advantages in terms of control and flexability, if you can afford it.
.>>
.>>Jeff Kesselman
.>
.>This is *not* true in general (in fact, I don't know of any frame buffer/
.>workstation for which it is true).
.>
.>The problem is that, though your frame buffer may generate video that
.>matches the NTSC timing parameters, it is RGB video, not NTSC.
.>A studio's sync generator will indeed lock its own sync to the computer's
.>sync, but there is no colour subcarrier coming out of the computer for
.>the studio's sync generator to lock to.  Thus colour subcarrier phase
.>will wander randomly with respect to sync.  (I know of no sync generator
.>that will lock its *subcarrier* output to a video input that contains
.>only sync.)

Well in Jeff's case it *IS* true, because the Amiga generates NTSC video
on its composite video output connector. Color subcarrier and everything.
It is however, in the case of the Amiga, easier to sync the Amiga to 
the studio than vice versa, you just feed in external sync to the RGB
connector. That is how the Amiga 1300 GenLock works, it syncs the Amiga
to the incoming video rather than trying to go the other way around. A
side effect of this is that the Genlock converts NTSC video into separate
RGB and sync, which I find kinda neat since I can watch TV on my RGB monitor
if I want to. 


--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.