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From: clldomps@cs.ruu.nl (Louis van Dompselaar)
Newsgroups: comp.graphics
Subject: Yamaha YJK colour system
Message-ID: <1991Apr08.095939.11144@cs.ruu.nl>
Date: 8 Apr 91 09:59:39 GMT
Organization: Utrecht University, Dept. of Computer Science
Lines: 39

Hi there!

I'm working with Yamaha's V9958 videochip which can generate 19268 colours
in only 64k of video RAM.

For those of you who are not familiar (I guess that's quite a lot :-) ),
here's how it works:

Colour selection is made with four pixels:


       7  6  5  4  3  2  1  0

Dot 0         Y1     |  KL
Dot 1         Y2     |  KH
Dot 2         Y3     |  JL
Dot 3         Y4     |  JH


The KL,KH,JL and JH values determine a kind-of 'base' colour, from
which each of the four pixels can differ with an intensity value Y.

The formulas are:

   Y = B/2 + R/4 + G/8

   J = R - Y

   K = G - Y


Anyway, the question is: given four pixels with each individual R,G and B
values, how to determine the correct J and K for these pixels and the
Y values for each pixel individually???

Thanks for any help

Louis van Dompselaar
clldomps@praxis.cs.ruu.nl