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Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!agate!pasteur!cory.Berkeley.EDU!johnhlee
From: johnhlee@cory.Berkeley.EDU (John Lee)
Newsgroups: comp.sys.amiga,comp.sys.amiga.tech
Subject: Chroma-key (was: Chaining Genlocks)
Message-ID: <15742@pasteur.Berkeley.EDU>
Date: 24 Jul 89 00:38:16 GMT
References: <367@cbnewsd.ATT.COM> <7245@cbmvax.UUCP>
Sender: news@pasteur.Berkeley.EDU
Reply-To: johnhlee@cory.Berkeley.EDU.UUCP (John Lee)
Organization: University of California, Berkeley
Lines: 25


 The discussion about genlocks has reminded me of an idea I had a while
 back.  Correct me if i'm wrong, but I believe (at least most) genlocks
 know when to inject live video in the output image (ie color 0) by a
 pin on the video port which changes state whenever the data coming out
 of the RGB lines is color zero.  ie, as the video image is scanned this
 pin goes high or low (i don't know which) when the background is being
 scanned.

 What I was thinking was this:  I remember that the old commodore genlock
 for the 1000 converted the incoming video to RGB and showed the genlocked
 image on the RGB passthru (since this is just an analog-to-analog conversion,
 this doesn't surprise me).  I don't know if any of the genlocks on the 
 market (or which) do this too.  The ones i've seen only have composite out.
 Anyway, if you built a little circuit which looked at the RGB signals on this
 line and outputted a digital signal depending on how "blue" the output was,
 you could feed this signal back into the genlock instead of the color0 line
 and have a primitive and CHEAP chroma-key.  True, you couldn't have any
 blue hues in your computer graphics, but whadda you want for (almost) free?

 Any replies?  would it be fast enough?  Please don't chastise me too much
 if i've said something dumb, though.

 - Vince Lee (now back from Europe), using my brother's account since
   berkeley doesn't think Mech E's deserve computer time.