## Displaying Spectra

### Displaying Spectra

I am interested in writing a program to calculate the transmission and
reflection spectra (transmitted and reflected optical power as a function
of wavelength) for thin film interference filters.  A useful feature would
be to "see" what the filter looks like; that is, to see what color it
would appear if I had the filter in my hand.  How can I map a calculated
spectrum to RGB or some other color coordinate system so that I can "see"
what a particular spectrum looks like?

Winston Chan

### Displaying Spectra

Quote:>would appear if I had the filter in my hand.  How can I map a calculated
>spectrum to RGB or some other color coordinate system so that I can "see"
>what a particular spectrum looks like?

Try this, firstly you could use the CIE system's standard colorimetric
observer, colour matching functions to calculate CIE XYZ tri stimulus
values, the colour matching functions are basically the spectral sens-
itivities of the human eye's three colour receptors - the retina's cones.

You can then do a matrix conversion from CIE XYZ to the RGB colour
space of your display, there are various ways of doing this, either see
the colour spaces FAQ or email me for the equations.

This should give you quite a good visual approximation of the filters
colours within the limitations of the gamut of your display and the
accuracy of the transformations used. (The more accurate XYZ -> RGB
transformations are more difficult).

Imaging Technology Research Group. University of Wesminster.

Hi, can anyone provide a pointer to an algorithm which will produce a
false-color representation of a range of integers?  I'm thinking of a
false-color spectrum representing elevation, like the one used in the recent
color digital elevation map created of MARS by laser rangefinding.

Essentially, the problem is this:  Given a normalized elevation range, say
from 1-256, is there a convenient algorithm available to produce RGB values
which will produce more-or-less visually equal spacing on a color "spectrum?"

I realize there is no simple straight path through the RGB color cube which
will produce a perfectly visually ordered transitional set of colors.  But is
there one that is even close?

Nick

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