Path: utzoo!attcan!utgpu!watmath!att!mcdchg!ddsw1!corpane!sparks
From: sparks@corpane.UUCP (John Sparks)
Newsgroups: comp.graphics
Subject: Re: How to map 24-bit RGB to best EGA/VGA palette?
Message-ID: <991@corpane.UUCP>
Date: 30 Aug 89 12:20:22 GMT
References: <3129@cbnewsm.ATT.COM> <7743@cbmvax.UUCP> <13319@well.UUCP>
Organization: Corpane Industries, Inc., Louisville Ky
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Organization: Corpane Industries, Inc.
Keywords: RGB EGA VGA color

In article <7771@cbmvax.UUCP> mitchell@cbmvax.UUCP (Fred Mitchell - QA) writes:
>In article <13381@well.UUCP> gors@well.UUCP (Michael Sierchio) writes:
>What you state is true, but you must keep in mind that we are going from
>16 million colors to 16 or 64 colors. The amount of error encountered would
>not be significant enough to be noticed at such a color quantization level.
>

You may have a *palette* of 16 million but the actual colors used in the
picture will generally be a lot less than that. You need to figure out exactly
how many tones are actually being used in the picture and go from there.
For example an 800 X 800 pixel image can only have at the most 640,000
different colors, and thats only if each pixel is a different color. Most
images will have a much smaller range of colors. The big problem is how to
convert 32 shades of blue (example) down to just 16 shades of blue. To keep
the picture from looking banded, you will have to dither the blues.

BTW: Maybe the thing to do is figure out how an Image Capture board
(framegrabber) figures out it's color palette when capturing a live scene.
The situation is the same, millions of real colors, condensed into a few.
One of the best products I've seen is the Digiview digitizer for the Amiga.
It uses a black and white camera and a color filter (Just like Voyager! :-)
And converts a full color scene into Amiga HAM mode (4096 colors) It has a
terrific dithering scheme. 

-- 
John Sparks   |  {rutgers|uunet}!ukma!corpane!sparks | D.I.S.K. 24hrs 1200bps
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A virtuous life is its own punishment.