[Radiance-general] Specularity Definition of Radiance Material

[Greg Ward]

Hi Andrei,

Actually, your original formula came through for me.  Maybe it got mangled on the way back to your inbox.

The formula you had for the specularity, where you divided by the "SCI" component, was correct if you use the Radiance "metal" primitive and apply the overall reflectance as your RGB values.  This is because the specular component is multiplied by the RGB color for metals.  I don't recommend using the "plastic" type in your case, but if you did, you would want to leave off the denominator as you say.

Cheers,
-Greg

> From: "Kolomenski, Andrei (JSC-SF311)[WYLE INTEG. SCI. & ENG.]" <andrei.kolomenski at nasa.gov>
> Subject: Re: [Radiance-general] Specularity Definition of Radiance Material
> Date: October 22, 2015 8:39:14 AM PDT
> 
> Hi Greg,
>  
> Thank you for your reply.
>  
> Unfortunately, as I pasted in the Specularity formula from MS Word into my original post, the division sign was lost in the process. The formula is intended to be a spectral power distribution (SPD) summation of the difference between a specular included (SCI) and a specular excluded (SCE) divided by the SCI.
>  
> This formula defines a relative specularity as a percentage of the total reflectance. As I understand, Radiance’s material specularity variable is the total specular reflectance normalized percentage, and not the relative specular percentage I was previously thinking.
>  
> So that: total reflectance = total specular reflectance + total diffuse reflectance
>  
> Using this methodology for a black material I compute a 5% Total Reflectance, and a 20% Relative Specularity, meaning that my Total Specular Reflectance is (5%*0.2) = 1%, and this value (0.01) is used to define Radiance’s specularity variable. Also, the Radiance RGB triplet is scaled by Total Reflectance (0.05).
>  
> Does this sound correct to you?
>  
> Thank you for the insight,
> Andrei Kolomenski
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