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From: forsythe@convex.com (Charles Forsythe)
Newsgroups: comp.graphics
Subject: Re: Colors of the Rainbow
Message-ID: <4347@convex.UUCP>
Date: 4 Jan 90 06:29:50 GMT
References: <2284@isaak.isa.de>
Sender: usenet@convex.UUCP
Lines: 32

schwarze@isaak.uucp (Jochen Schwarze) writes:
>I'm looking for a function that maps a wavelength to the appropriate RGB
>triple. Has anybody done this? Any pointers appreciated.

This is actually very easy to do.

R = M * sin(T) + N
G = M * sin(T + phi) + N
B = M * sin(T + theta) + N

T goes from 0 to 360 degress.
phi is 120 degrees
theta is 240 degrees

M and N are just adjustment constants, typically M=128 and N=128 to swing
over an entire unsigned 8-bit value.  I haven't done this for a while, but
I know that the sine waves should be evenly phase-shifted across an interval.
I'm pretty sure it's 360 degrees, but it might be 180 -- try and see.  This
should go dark_red-->purple with all of the colors inbetween in their proper
order.

One problem with this color set is that it's luminosity is constant.  While
the colors are vibrant, there is no contrast and hence an image using just these
colors can be a little boring.  If it's important, you may want to experiment
with some functions that add or subtract luminoisity and saturation to add
a little more diversity to the hues.

-Charles
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