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From: olsen@hpfcdq.HP.COM (John Olsen)
Newsgroups: comp.sys.amiga
Subject: Re: Graphics standards and super-graphics s/w
Message-ID: <4710010@hpfcdq.HP.COM>
Date: 6 Mar 90 15:46:29 GMT
References: <1654@crash.cts.com>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 30

krag@cup.portal.com (Kevin Ray Grotjohn) writes:
>Has anyone seen the TurboColors hack.  I swear it allows 29,000 + colors
>with 30 shades of RGB rather than 16 without flickering or dithering.
>How do they do that with only 4 bit video dacs.

It's really not that tough.  All you need to do is open two non-interlace
screens and swap between them every refresh.  That way, you can use color 
00f (bright blue) on one screen, and at the same position on the other 
screen you use 00e (nearly bright blue).  What you see on the screen is 
about halfway between the two, magically giving you 30 shades of the 
primary colors (not counting black) by using shades half-way between the
existing shades.

You can possibly get more shades if you don't use adjacent color values, but 
the flicker would soon become noticeable.  With nearly-identical values, the
flicker should be hard to see even for those who are driven nuts by interlace.

(For you techno-weenies, the additional (>30) shades would show up 
because the brightness values are non-linear, so adding color 003 to 
00b doesn't necessarily average out to create 007.  The bad news is that
results may not be repeatable over larger spreads like that.)

Also, you could use interlaced screens, but you would end up swapping every 
1/30 second instead of 1/60 which might also add to the flicker problem.
(Swapping between two interlaced screens?  Eech!)

John M. Olsen, Graphics Software Engineer
olsen@hpfcdq.HP.COM  -or-  ...!hplabs!hpfcdq!olsen
(W) Hewlett-Packard, MS 73, 3404 E. Harmony Road, Ft Collins, CO 80525
(H) 700 E. Drake Rd. #E12, Ft Collins, CO 80525