Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!caip!topaz!ll-xn!nike!ucbcad!ucbvax!disunix.UUCP!jhs
From: jhs@disunix.UUCP
Newsgroups: net.micro.atari16
Subject: Re: 520st composit output
Message-ID: <8607022017.AA02840@mitre-bedford.ARPA>
Date: Wed, 2-Jul-86 16:17:48 EDT
Article-I.D.: mitre-be.8607022017.AA02840
Posted: Wed Jul  2 16:17:48 1986
Date-Received: Thu, 3-Jul-86 07:31:04 EDT
References: <860701-162634-4288@Xerox>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The MITRE Corp., Bedford, MA
Lines: 28

Composite signals are made by black magic to fit into a nominal 6 MHz TV
channel -- in fact I believe the video portion has to fit into 4.5 MHz.
To do this it is necessary to low-pass filter the luminance signal to leave
room for the chroma signal, and also to bandpass filter the chroma (or lowpass
filter it in baseband form before putting it on the color subcarrier).
Anyway, these lowpass operations amount to smearing of detail in the picture
or intentionally limiting resolution.  Apparently the chroma suffers the
worst, which is why in color TV pictures the red areas sometimes appear to be
painted on sloppily so they spill outside the area that was supposed to be
red.

If you could get the baseband luminance signal out of the Atari before it has
been filtered, you might get the resolution you desire.  I have no data on the
circuit, but maybe somebody out there knows if this signal is available to be
brought out.  I speculate that it may be available somewhere over on the
monochrome monitor output.  If it is still active somewhere even when you have
plugged into the other jack, you may be able to get access to it.

Too bad they didn't provide an option of 60-Hz standard monochrome output as
well as composite.

The other trick that comes to mind is to run your monochrome monitor off the
GREEN output of the RGB output.  That is supposed to give a reasonable
monochrome picture for most normal scenes.

Good luck.

-John Sangster / jhs@mitre-bedford.arpa