# making material

Holle,my name is kouichi in Japanese !

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
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.

Supposing it meets, I can understand.

Thanks a lot.

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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:

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: 小林 紘一 <[email protected]>
Date: Thu Nov 13, 2003 6:53:04 AM US/Pacific
To: [email protected]

Holle,my name is kouichi in Japanese !

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
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.