[Radiance-general] which basis for xy to RGB conversion in lamp.tab?

[Gregory J. Ward]

Hi Christian,

> If i use ies2rad with the '-t' option referring to a specified  
> lamp, how are the x,y values in 'lamp.tab' transfered into RGB? Is  
> the basis 'color.h'?  If i change the white point of color.h into  
> D65 nothing changes within the RGB values.

The ies2rad program should convert the xyY value in the lamp.tab file  
to a Radiance RGB multiplier for the source.  The Y value in lamp.tab  
is the lumen depreciation factor.

Changing the white point in the _second_ set of primaries in color.h  
(not the first set, which is only used if NTSC is defined), should  
definitely affect the output of ies2rad, but you would have to rerun  
"rmake install" in the src/common directory, then remove ies2rad and  
run "rmake install" in the src/cv directory (in that order).

> On the other hand, if i calculate the RGB (D65)  values on my own,  
> assuming Y=1, i get not the right illuminance value after applying  
> rtrace and rcalc with the correct factors. e.g. $ echo "0 0 0 0 0  
> 1" |rtrace -I -h lux_test.oct | rcalc -e '$1=179*(.22200431*$1+. 
> 70665477*$2+.07134092*$3)'

It should work.  You would have to give more details about how your  
value was unexpected, or your scene files.

-Greg