[Radiance-general] Create constant radiance image

[John Mardaljevic]

> There is no agreed-upon weighting for radiance values, only luminance

Of course (duh)!  I get so used to working between irradiance and  
illuminance using luminous efficacy models that I occasionally forget  
some of the R(r)adiance basics.  Nonetheless, to avoid confusion in  
the future, might I suggest an update to the ximage manpage?  Perhaps  
something like:

<return> 		Display the mean RGB radiance averaged over the area of  
interest.  [For a single value, the mean seems less arbitrary than the  
maximum value for any one of the channels.  Otherwise, some indication  
of what the current behaviour is.]
l 			Display the photometrically-weighted RGB luminance value in the  
area of interest. This assumes that the image was correctly computed  
in terms of luminance.
Then again, if I'm the only person who's been bamboozled by this, it's  
probably not worth the mods to the man page.
-John
-----------------------------------------------
Dr. John Mardaljevic
Reader in Daylight Modelling
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