POV-Ray : Newsgroups : povray.text.tutorials : Highlight Voodo : Re: Highlight Voodo Server Time
5 Dec 2022 13:58:06 EST (-0500)
  Re: Highlight Voodo  
From: clipka
Date: 4 Jul 2012 19:24:17
Message: <4ff4d0a1$1@news.povray.org>
Am 04.07.2012 23:27, schrieb Cousin Ricky:
> clipka<ano### [at] anonymousorg>  wrote:
>> Instead, for a polished material, a value of
>>
>>       specular 0.25 * ((1/ROUGHNESS)+1) * REFLECTION
>>
>> or
>>
>>       phong 0.5 * (PHONG_SIZE + 1) * REFLECTION
>>
>> is actually realistic, [...]
>
> How is this relationship affected if the material isn't "polished"?

Mu. POV-Ray's reflection is only realistic for polished surfaces.

> How is this affected by variable or fresnel reflection?

Phong and specular currently don't respect fresnel's law, so when using 
fresnel reflection you should reduce the specular or phong parameter a 
bit to compensate; it's not the real thing though.

> Is there any relationship between reflection and roughness/phong_size?

If we're talking about polished surfaces: Yes, obviously there is a 
relationship - it's in the formulae given above.

If we're talking about dull surfaces, then mu - as stated above, POV-Ray 
does not natively support dull (aka blurred) reflections.

>> BTW there's also a similar law goverining the "diffuse" parameter: If
>> you set "brilliance" to anything but 1, you should set "diffuse" to a
>> maximum of
>>
>>       diffuse 0.5 * (BRILLIANCE + 1)
>>
>> which would correspond to a diffuse reflection of 100%.
>
> Does this mean that you can set diffuse>  1 if brilliance is>  1?

Well, you /can/ do that regardless of brilliance, except that it would 
be unrealistic at brilliance = 1; but for a material with brilliance 2, 
diffuse 1.2 isn't unrealistic.

> In metals.inc and golds.inc, brilliance is increased as reflection is increased.
>   Is there such a correlation in reality, or was that just the way it was decided
> to define the textures?

That's just the way they did it. There's not much parameterization in 
metals.inc or golds.inc that has any correlation to reality whatsoever - 
the material parameters were chosen solely for artistic reasons.


BTW, by now POV-Ray has acquired some new syntax to automatically do the 
above computations for you: Specifying

     specular albedo SPECULAR_ALBEDO
     roughness ROUGHNESS

     phong albedo PHONG_ALBEDO
     phong_size PHONG_SIZE

     diffuse albedo DIFFUSE_ALBEDO
     brilliance BRILLIANCE

is equivalent to:

     specular 0.25 * ((1/ROUGHNESS)+1) * SPECULAR_ALBEDO
     roughness ROUGHNESS

     phong 0.5 * (PHONG_SIZE + 1) * PHONG_ALBEDO
     phong_size PHONG_SIZE

     diffuse 0.5 * (BRILLIANCE + 1) * DIFFUSE_ALBEDO
     brilliance BRILLIANCE

Specular and phong albedo should be equal to reflection (for polished 
materials), while the sum of reflection and diffuse albedo should be 1 
or lower.

(Fresnel (or variable) reflection equivalent is still not supported for 
highlights though, and significantly dull reflection is still not 
available out of the box.)


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