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Subject: Re: Using colour to indicate response intensity



David White wrote:

> Plenty of people must have to do this, e.g., weather maps that use
> colour to indicate rainfall intensity. Is there a "standard"
> algorithm that takes a single number in a suitable range and outputs
> the corresponding RGB value for a linear rather than circular colour
> progression?

No. There are *lots* of ways of doing such "false-colour", a.k.a.
colour-mapped plots. From algebraic methods that compute each
coordinate in a colour-space directly from the input value, such as:

# assuming 'val' has already been normalized to [0..1]
(H,S,V) = (0.1 + val*0.8, 1, 1)
(R,G,B) = (val, 1-val, 2*abs(val-0.5))

to techniques based on distrete palettes (with or without
interpolation). To get an impression what's possible, you could
experiment a bit with programs for drawing fractal images like
'fractint', or check out gnuplot's "pm3d" plotting mode.

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

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