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From: cmcmanis@sun.uucp (Chuck McManis)
Newsgroups: comp.sys.atari.st
Subject: Re: RGB to video composite for ATARI 1040/Mega ST computer.
Message-ID: <17973@sun.uucp>
Date: Mon, 4-May-87 15:03:46 EDT
Article-I.D.: sun.17973
Posted: Mon May  4 15:03:46 1987
Date-Received: Tue, 5-May-87 05:29:32 EDT
References: <8705021243.AA24169@cogsci.berkeley.edu> <1987May4.010515.18712@gpu.utcs.toronto.edu>
Organization: Sun Microsystems, Inc. - Mtn View, CA
Lines: 58
Keywords: Hardware box wanted for converting RGB to composite video.
Summary: RGB -> Composite != Genlock

In another article, (Peter Santangeli) responds to :
> An article Bryce Nesbitt wrote, which said :
>> 3>  Fancy stuff that (unfortunately) only the Amiga has.  This includes
>>     genlocking inputs so that the Amiga can sync to an external source (for
>>     overlays etc.).  
> Hate to put a damper on your amiga worshiping, but the ST DOES
> allow FULL EXTERNAL SYNC. This feature was included specificallyu
> for this kind of work. Only facts eh?

This is news to me, and I have kept a fairly close watch on the two computers.
My question is this, are these external syncs available at one of the
video connectors ?  Or do I have to run wires into the box somewhere ?
 
>>In answer to the actual question asked:  Yes RGB to composite converters are
>>made.  I do not have any details on where and how.  These could be adapted
>>with a minimum of soldering to fit on a Mega St.
> Also, if you are at all handy with a soldering Iron, a very good
> simple interface design is available in the Public Domain from Anees
> Munshi at U of T. Also, I have heard that several German companies
> are offering exactly the interface you desire.
> Pete

Correct, I have seen the composite video circuit described above. The
unique ability of the Amiga is/was (whatever) Genlock. This means the
Amiga can sync to an external video signal and mix it's graphics with
the video of the external source. What is required for this capability
is external sync for the Amiga graphics and a 'smart' switch that knows
to use external video when the Amiga is 'displaying' color 0. And then to
take this mixed video and produce a composite out to be recorded on the
tape deck. Note that it is possible to do chroma-key type stuff externally
where an external mixer looks for a given hue and replaces it with video 
from a separate source, thats how they do the weather maps on tv, by 
replacing everything 'blue' in the picture with the weather map. (It is
really interesting if the weatherman is wearing a blue tie!) 

Now on the Amiga, since the hardware is 'expecting' a GenLock interface
it has some hooks built in for that. Consequently the GenLock add on is
relativly inexpensive, its biggest job is to convert composite video to
RGB so that it can be displayed on the Amiga screen and the user can see
what the output will look like. List price for a Genlock interface is $299.
To do chroma keying requres a video mixer with chroma key as an option.
I believe Recoton sells one of these for $1800. If the Atari cannot be
sync'd to NTSC sync timings you will also need a timebase corrector
which goes for about $800. This will be essential if you wish to use
the Atari High resolution monochrome mode. 

Now given the context of this *single* application, one can say the 
Amiga is better for *Video Titling* than the Atari ST. And if I may
be so bold as to say that this is the *only* way to compare systems.
Is it better for *your* particular application. Anyway I look 
forward for specifics to how the Atari External sync is used.


-- 
--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These views are my own and no one elses. They could be yours too, just
call MrgCop() and then ReThinkDisplay()!