[Radiance-general] 3.8 Falsecolor Scale

[John Mardaljevic]

Rob,

> expect blue to represent the lowest and
> red to represent the most intense values

I beg to differ.  When I first decided on a false-colour scale (quite  
some years ago) I had about 15 to choose from in IDL (data analysis/ 
visualisation package similar to MATLAB).   The one they called  
"gamma" (black-blue-red-orange-yellow-white) seemed a natural since  
it corresponded to my expectations (i.e. cold through to hot).  I've  
been using it ever since.  I clip the scale to go from the brightest  
blue through to yellow.  I clip at the low end because part of the  
black to blue transition looks a little too close to the blue-red  
transition.  White at the top is removed so that high values in  
figures wouldn't bleed into background white paper on hard copies.   
Example:

http://www.iesd.dmu.ac.uk/~jm/pickup/pipe_figure.pdf

I certainly prefers Greg's new scale to the previous version.   
However I will continue to use my gamma scale even though it offers  
less discrimination than Greg's new scale.  I guess I just prefer a  
simple thermal scale.  The only other scale I use in IDL is a red- 
green-blue scale whenever I need to show values either side of zero  
(e.g. the difference between two images).

I suspect the red=high expectation originates with the common  
red=danger/warning usage.  Plus the fact that the red light in a  
traffic signal is always at the top (any exceptions?).  These are of  
course uses of colour in a discrete rather than continuous sense.   
Indeed, whilst red=danger etc. does lead to an expectation that red  
should be the colour for the most intense values (i.e. at the top), I  
don't believe that there is any intuitive expectation for what should  
be below [1].  Or, how the transitions should look.  The rainbow  
scale provides a "natural" solution of sorts.  However, despite a  
training in physics and a familiarity with the progression of colours  
in a rainbow, I still find the thermal scale more of an intuitive  
progression than the rainbow scale.  Whilst I don't see too many  
examples I'm not entirely alone in having this preference: the false- 
colour scheme used in ECOTECT seems similar.

-John

[1] Those familiar with Doppler broadening of spectral lines (where  
the line is both red and blue shifted) excepted.

-----------------------------------------------
Dr. John Mardaljevic
Senior Research Fellow
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972
+44 (0) 116 257 7981 (fax)

jm at dmu.ac.uk
http://www.iesd.dmu.ac.uk/~jm