[Radiance-general] Specularity Definition of Radiance Material

[Greg Ward]

Hi Andrei,

While specularities greater than 0.1 are not realistic for non-metals, specularity is limited only by physicality (i.e., 1.0) for metals.

Your method should work well enough for metallic surfaces with uncolored highlights.  If you have colored specular reflections, then you may have to do something a little more sophisticated, like multiplying the CIE standard observer curves to get XYZ then convert to RGB for Radiance using xyz_rgb.cal.

Cheers,
-Greg

> From: "Kolomenski, Andrei (JSC-SF311)[WYLE INTEG. SCI. & ENG.]" <andrei.kolomenski at nasa.gov>
> Subject: [Radiance-general] Specularity Definition of Radiance Material
> Date: October 20, 2015 2:08:10 PM PDT
> 
> Hello Radiance Experts,
>  
> I have used a Hemispherical Spectral Reflectance meter to measure the Specular Included (SCI) and Specular Excluded (SCE) SPDs of a material. The obtained SPDs are in the range of 360 to 740 nm., commonly considered the photopic range. Then I compute the total photopic specularity using the equation below.
>  
> 
>  
>  
> For a black shiny metal sample, I compute a specularity of 21%. Is it correct to use a value of 0.21 for my specularity definition of a metal material primitive. I’ve read that specularity values greater than  0.1 are not realistic (http://radsite.lbl.gov/radiance/refer/ray.html#Materials) in Radiance. In the .hdr rendered image, the material appears to be highly specular to the degree that it acts like a mirror. So this why I’m concerned if I’m using the right procedure to define the specularity for the Radiance metal primitive.
>  
> Is it correct to use a hemispherical reflectance meter, and the equation above to define the Radiance specularity term.
>  
> Thank you for your input,
> Andrei Kolomenski
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