Inspired by N. Conway's post, I got to thinking about how radiosity interacts
(or IMHO should interact) with the surface diffuse.

Basically, if anyone can spot any misconceptions, or fill in the gaps, in what
follows, please do so. Please.

A white rough surface will have a diffuse of 1, since all light is diffusely
reflected.
A black rough surface will also have a diffuse of 1, since all light is
absorbed, rather than reflected.
A reflective surface should have its diffuse + reflection component adding to 1.

The amount of light diffusely reflected by an object (and therefore used in
radiosity calculations) is: (1-reflection) * rgb - i.e. if a surface is 0.5
reflective, you should set the diffuse to 0.5

Now, the only other thing I can't quite work out is that, if specular highlights
are just another form of reflection, how do you adjust diffuse to take account
of a particular specular setting?

(btw my brain is small - I'm not really considering any colours except black,
white and gray here)


--
#macro A(V,B,C,R)#while(B-256)#if(V-128/B>=0)sphere{0,.5translate<C-4R-1,9>
pigment{rgb<1-C/8R/2C/8>}}#local V=V-128/B;#end#local B=B*2;#local C=C+1;#
end#end A(234,1,0,2)A(85,1,0,1)A(81,1,0,0)light_source{-5 1}//Tom Melly

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> The amount of light diffusely reflected by an object (and therefore used
in
> radiosity calculations) is: (1-reflection) * rgb - i.e. if a surface is
0.5
> reflective, you should set the diffuse to 0.5

I don't believe this restriction is built in. (I may be wrong.) I think, if
you choose to set reflection and diffuse such that they add up to 1, you're
welcome to do so, and the amount of light calculated coming from that object
will be .5*pigment color + .5*reflected light color (if you set them both to
.5). Specular highlights are merely added to that value. Remember that there
is no upper limit to colors of light in POV-Ray, "1" is an artificial limit
that we tend to put in our scenes. (A scene with light sources emitting 100
light would be perfectly physically realistic. Of course, it would only be
viewable through a filtered lens (a sphere with color rgbf<1,1,1,.01>).)

 - Slime
[ http://www.slimeland.com/ ]

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Tom Melly wrote:
> 
> A white rough surface will have a diffuse of 1, since all light is diffusely
> reflected.
> A black rough surface will also have a diffuse of 1, since all light is
> absorbed, rather than reflected.
> A reflective surface should have its diffuse + reflection component adding to 1.

In theory, a black surface would have a very low diffuse reflection, 
because it's not, in fact, actually reflecting the light at all. 
However, because POV-Ray separates diffuse from pigment while in real 
life these properties are combined, this is a perfectly correct and 
reasonable way to do it.. and yes, you will get more realistic 
reflections and lighting if diffuse + reflection = 1.

> Now, the only other thing I can't quite work out is that, if specular highlights
> are just another form of reflection, how do you adjust diffuse to take account
> of a particular specular setting?

Specular highlights in POV-Ray are a kind of kludge. In real life, 
specular highlights are simply reflections of light sources and other 
really bright things. In POV-Ray, these can be accurately simulated by 
using "real" light sources (as opposed to point lights, which of course 
can't be reflected) with a realistically high brightness, and giving 
every object some amount of (possibly blurred) reflection.

Obviously, even if we CAN do this, we don't always want to, because it's 
really damn slow, and might produce results no better than we'd get with 
some specular highlights artificially added in.

That's the long answer. The short answer is: "ignore specular values in 
your calculations."

-Xplo

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