[Radiance-general] Spectrophotometer Data to Radiance Surface Descriptions

[Greg Ward]

Hi Randolph,

I believe I had a script or .cal file or something at one time to  
compute the specularity from separate "specular included" and  
"specular excluded" measurements, but I can't find it.  The  
calculation is pretty simple, though.  Just subtract the "excluded"  
from the "included" Y values and divide by the the "included" Y  
measurement to get the specular percentage for a metallic material  
with colored highlights.  For a plastic material, the specular  
fraction is the "included" minus the "excluded" Y over 100 (assuming a  
0-100% scale for Y).

The material color is the "included" Yxy converted to RGB for metal,  
and the "excluded" Yxy converted to RGB for plastic.  The conversions  
are given in ray/src/cal/cal/xyz_rgb.cal.  You can quickly spit out  
the matrix coefficients for this conversion using:

	rcalc -n -f xyz_rgb.cal -o cmat.fmt

Best,
-Greg

> From: R Fritz <RFritz at lbl.gov>
> Date: July 26, 2010 12:59:59 PM PDT
>
> If I have diffuse and specular XYZ surface data from a  
> spectrophotometer—six numbers—, how do I convert that into Radiance  
> material descriptions? Can I calculate the "specularity" for types  
> plastic and metal from that data? Or do I need to use a function or  
> data-based material type?