Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.graphics
Subject: Re: Amiga Display Resolution Modes.
Message-ID: <18028@cbmvax.commodore.com>
Date: 24 Jan 91 21:31:46 GMT
References: <1991Jan14.024715.1@ccvax.iastate.edu> <1991Jan16.231956.1939@agora.rain.com> <188daf2b.ARN010c@omega.ruhr.de> <1991Jan22.194356.1@ccvax.iastate.edu>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 44

In article <1991Jan22.194356.1@ccvax.iastate.edu> taab5@ccvax.iastate.edu (Marc Barrett) writes:
>In article <188daf2b.ARN010c@omega.ruhr.de>, alpha@omega.ruhr.de (Rudolf Neuhaus) writes:
>> In article <1991Jan16.231956.1939@agora.rain.com>, Bill Seymour writes:

>>> 	Some mention should be made here of the 'every other pixel' display
>>> that the 2320 and 3000/VGA gives you in SuperHighRes modes. Although the
>>> percieved resolution is 1280x200/256/400/512, the actual display is still
>>> 640 pixel wide. They just display every other pixel...

>> Are you sure about that? Couldn't it just be your monitor, ..

>   The Super Denise puts out 1280xXXX video in SuperHires mode.  However,
>when you turn the Display Enhancer in the A3000 on, the Display Enhancer
>only samples every other pixel in SuperHiRes mode.  The result is as
>described above.  It is due to the Display Enhancer, and NOT the monitor.

That's correct.

The display enhancer is in effect a real-time digitizer.  Being a digital
device, it has a particular sampling rate, and can only deal with pixels at
that rate (70ns per pixel) or lower (such as the lores modes).  If you feed
it 35ns pixels, it will only get every other pixel.  It does know about 
different display rates, so if it sees a 31kHz scan rate coming it, it will
automatically get out of the way.  The 1280xN modes are 15kHz, but with
35ns pixels, so they wind up generating this strange every-other-pixel
output.  Which is the best you can do with that resolution on a VGA monitor
anyway.  For a multisync, you simply flick the bypass switch on the converter
and get the proper expression of the 1280xN modes on your monitor.

Monitors, from a cheap TV all the way up to your expensive new multi-whatever,
are analog devices.  There's no physical concept of pixels across the screen,
only a rough limit on how many pixel changes per line can be clearly seen.
For example, while you can't read 8 point text generated in the 1280xN mode on
a TV set, you can tell the difference between titling done in the 1280xN
mode vs. a 680xN mode.  Really hot commercial titling boxes may go to 2000 or
so pixels across (in TV terms, meaning overscan, this Amiga mode is really
around 1400 pixels across).  Not to be individually resolved, but so that 
curves can come in much smoother.  Additional colors, for antialiasing such
lines, also makes such titles clearer.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	"What works for me might work for you"	-Jimmy Buffett