[Radiance-general] making material

[Greg Ward]

Hello Kouichi,

It appears that page 310 (sect. 5.1.14) does contain an error because 
it does not convert luminance (in cd/m^2) to radiance (in watts/sr/m^2) 
using the 1/179 factor.  The formulas in the previous section (5.1.13) 
are correct, but the next section neglects the 179 lumens/watt scaling. 
  We apologize for this oversight.

Regarding the best way to get correct colors, I strongly encourage you 
to read the paper I coauthored at last year's Eurographics Workshop on 
Rendering, which you can find here:

	http://www.anyhere.com/gward/papers/egwr02/

This explains how you really want to convolve the source spectrum with 
the surface reflectance spectra and white balance the results.  Without 
such a technique, you are better off simply using white light sources, 
even when you know they are not truly white.

I hope this helps.
-Greg

> From: $B>.NS(B $B9I0l(B <kouichi_any@hotmail.com>
> Date: Thu Nov 13, 2003  6:53:04  AM US/Pacific
> To: radiance-general@radiance-online.org
>
> Holle,my name is kouichi in Japanese !
> I'm using Rad for win with Autocad.
>
> I have some questions.
>
> Firstly,when I make  non-luminous material  like a plastic, I  use 
> xyz_rgb.cal with reflectance(Y) and chromaticity(x y)  mesured by 
> reflectance meter. Is this OK ?
>
> And secondly, For luminous material  like a light, if uncolored , I 
> use { Radiance =luminance/179} and {Radiance= Rr = Rb = Rg}.
> But if colored materials ,I want to use  xyz_rgb.cal with luminance 
> and chromaticity(x y)  mesured by luminance meter.In this cace , 
> Y=luminance?
> In page 310 of Rendering with Radiance (5.1.14) ;
>
> If our device mesure an xyY value of (.424 .399 63 ), these cordinates 
> can be converted to RGB using xyz_rag.cal:
> % rcalc -f xyz_rgb.cal  -e 'ix=$1;iy=$2;iY=$3'  -f xyz_rgb.cal \
> -e 'iX=ix/iy*iY;iZ=(1-ix-iy)/iy*iY'  \
> -e '$1=R(iX,iY,iZ) ; $2=G(iX,iY,Z) ; $3=B(iX,iY,iZ)'
> .424 .399 63
>
> and output is  ( 87.0934196  57.4293016  22.034743 ).
>
> And in p311;
>
> void light halogen_light
> 0
> 0
> 3  87.0934196  57.4293016  22.034743
>
>
> I have thought  Y=luminance.But 63(cd/m2) is too small for halogen 
> light.
> And using {.265r +.655b+ .082b} with three radiance value for 
> halogen_light, output is 63.
> Is 63 Radiance(=luminance/179)??
>
> Supposing it meets, I can understand.
>
> Thanks a lot.