wavelength to RGB ???

Sergei O. Naoumov wrote on Jul 07, 1998

Hi!
I was wondering whether anyone did this excercise before: I have a
range of visible wavelengths, say from 3000 to 8000 angstroms, and
I want to express it in terms of RGB numbers to display on a 8 bit
depth screen.

It does not seem like lambda is a simple linear combination of the
red, green and blue because one can have different combinations of
the coefficients to get the same lambda.

Any advice?

Thanks much,
			Sergei

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Doug Tody wrote on Jul 07, 1998

> I was wondering whether anyone did this excercise before: I have a
> range of visible wavelengths, say from 3000 to 8000 angstroms, and
> I want to express it in terms of RGB numbers to display on a 8 bit
> depth screen.
> 
> It does not seem like lambda is a simple linear combination of the
> red, green and blue because one can have different combinations of
> the coefficients to get the same lambda.

> Any advice?

Sergei, this sounds like the usual pseudocolor rendering problem encountered
when displaying grayscale data (i.e. a linear range of values) as some
range of RGB color values.  In principle in a case such as you describe
one could try to map a visible wavelength to a color using a physical
color spectrum mapping, but in practice this rarely works well on a
workstation screen for various reasons, and a pseudocolor (nonphysical)
mapping is used instead.  You might want to have a look at some pseudocolor
color tables to see if any will render the data the way you want.  For
example, see the collection of colortables in ximtool/luts in the x11iraf
distribution (this is often installed with ximtool as well).  A separate
copy of this is available as

    ftp://iraf.noao.edu/iraf/x11iraf/imtoolcmap.tar

These are normalized colormaps, you just scale them linearly to fit your
data range.

	- Doug

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Last post on Jul 07, 1998