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Subject: Re: Using colour to indicate response intensity



David White wrote:

> Thanks to everyone for their replies. I'll check out the references
> suggested. FYI, the application is the display of intensities read
> out of an instrument (e.g., corresponding to the concentration of
> some element) and are displayed on a 2D graph (X = time, Y = element
> mass). The intensity, or colour, is the third dimension, and we
> expect to see islands of colour that change from the edge to the
> centre.

In that case, let me repreat my hint: there's no need to re-invent
this wheel all for yourself. There's plenty existing programs,
including free software, that do this for you. gnuplot since version
4.0, e.g. It also has a whole collection of proven usable colour
mapping functions for you.

> My first thought was to link the intensity directly to colour
> wavelength, so you'd get a rainbow progression (in which,
> conveniently, the blue end means cool or low, and the red end means
> hot or high).

That would be rather over-complicated, and for a sub-optimal result at
that. The real rainbow is physically linear, but not perceptibly.
I.e. the eye is not evolved to linearly resolve rainbow colours.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

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