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From: doug@xdos.UUCP (Doug Merritt)
Newsgroups: comp.sys.amiga.tech
Subject: Nonlinear video info?
Summary: Got any?
Message-ID: <596@xdos.UUCP>
Date: 2 Jan 90 04:20:36 GMT
Reply-To: doug@xdos.UUCP (Doug Merritt)
Organization: Hunter Systems, Mountain View CA (Silicon Valley)
Lines: 44

I just finished a dithering project for face server images (starting
with a program by Thad Floryan). Using a simple 2x2 ordered dither
in a high res screen and assuming a linear grey scale for the 4
bit planes, I ended up with 61 grey scales (15 * 4 + 1).

I then decided to try compensating the grey scale for nonlinearity
(as suggested by "Digital Halftoning"). In the process it occurred
to me that I could get more grey levels by taking advantage of the
nonlinearity.

After several days of tedious trial-and-error hacking on the grey scale,
I succeeded in creating one that has around 180 unique dithered grey levels,
producing a significant improvement in the resolution of the image.

The question: does anyone out there have any information about the
nonlinearity of the Amiga video output? This trial and error stuff is
for the birds! I stopped because I got burnt out in the process of
creating *any* nearly-monotonic grey scale, not because I had
created the best possible scale.

Second question: I've never heard of anyone doing this before on *any*
kind of equipment. Have you? Is it common, and I simply missed it?
It seems like a valuable way of improving output quality. The "Digital
Halftoning" bible glosses over the whole subjects of nonlinearity
and grey scales as trivial, but they're not. I suspect he just ran out
of steam.

Finally, yes, I know that different monitors are nonlinear in different
ways, too, but hey, I'm doing the best I can, and I don't have any info
about variation in nonlinearity from one monitor to another, either, so
I was just eyeballing it on my setup and leaving it at that. No, I don't
have a photometer, and if I did I'd worry about *its* linearity.

(And as for using ordered dither, I know about Floyd-Steinberg, but that's
a minor difference compared with what I could get from improving the
linearity of the grey scale! Also my original motivation for this project
was simply speed, which I've achieved...50 fold faster than the original
display program. Gee, it's hard to do fast graphics without the blitter!
But satisfying.)
	Thanks,
		Doug
-- 
Doug Merritt		{pyramid,apple}!xdos!doug
Member, Crusaders for a Better Tomorrow		Professional Wildeyed Visionary