[Radiance-general] Re: Multi spectral rendering

[Greg Ward]

Hi Andrew,

Since we needed to make exact comparisons between rendered images by 
pixel subtraction, I gave up on my efforts to run Radiance many times 
for spectral sampling, and we used my coauthor's (Elena's) Monte Carlo 
ray-tracer, instead.  If regenerating the exact samples isn't an issue 
for you, you probably can run Radiance many times, however, and others 
have done this.

The best way to do it for non-human consumption is to defined many 
materials files, one for every three samples, and render from these in 
a for loop.  The only place RGB is assumed in the code is when it's 
combining primaries to get brightness for a weight test or somesuch, 
and it shouldn't affect the result much for adjacent samples, which 
should be fairly similar.

Good luck!
-Greg

> From: Andrew Bettison <andrewb@acres.com.au>
> Date: Thu Jun 19, 2003  12:50:14  AM US/Pacific
>
> Greg,
>
> In your paper to the 2002 Eutographics Workshop on Rendering, you 
> compare sRGB and Sharp RGB renderings against a multi-spectral 
> rendering at 69 evenly-spaced spectral samples from 380 to 720 nm.  I 
> am curious how you made that multi-spectral rendering.  Did you divide 
> the 69 wavelengths into groups of three and run rpict(1) 23 times?  Or 
> did you run rpict(1) 69 times with proportional R, G, and B values?  
> Or did you hack rpict(1) from a 3-band renderer to a 69-band one?
>
> In the first case, wouldn�t there have been issues with gradient 
> interpolation, which is calculated using the CIE definition of 
> brightness from R, G, and B?  Also adaptive shadow testing?  I am 
> currently wrestling with these issues as I have to perform 
> multi-spectral renderings of many more than 69 bands from 380 nm to 14 
> microns, so the CIE definition of brightness won't do.
>
> --
> Andrew Bettison
> Acacia Research Pty Ltd