> The light that scatters less will indeed come out nearer to "white", but
> its direction is as random as any other light that manages to come back
> out. (At least that's true for most solid materials, in which the
> scattering is sufficiently anisotropic.)

OK that was the fact I was missing in my analysis. I didn't expect it 
was a digital difference between surface reflection rays emerging at a 
specific angle and then "reflection" rays from just under the surface at 
completely random angle. I had assumed it was some kind of transition 
between the two.

> - It doesn't properly handle the variation in specular reflection
> depending on incoming angle and ior (modeled by the "fresnel" setting
> for reflections).

Do you mean the specular reflections for point light sources controlled 
by the specular keyword? Or the specular reflections you get by using 
the reflection and power parameters (which the fresnel setting has an 
effect on)?

> - MCPov gets diffuse reflections wrong by a factor of 2.

Can I correct for this by simply halving the diffuse factor in the 
finish statement?

> - When using a "brilliance" setting of something other than 1.0, the
> value specified in "diffuse" is /not/ the percentage of light scattered
> back diffusely. Instead, the "diffuse" parameter directly controls the
> brightness of the brightest spot. The new "albedo" keyword takes care of
> this discrepancy: If you specify "diffuse albedo X", then X is indeed
> the ratio of light scattered back diffusely (of all the light that comes
> in).

OK, I've not played about with brilliance before - but I assume albedo 
is not part of mcpov.

> As you can see there are still some details missing for physically
> realistic materials. But I'll keep working on it.

Do you have an idea how much work it is to get mcpov type rendering into 
3.7? Currently I use a simple program that fires off multiple mcpov 
instances and then merges the results, which works ok but obviously it 
doesn't take advantage of all the other goodies in 3.7.

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