>   I don't believe unbiasing makes surfaces more opaque
> 

It could very well be the case. The unbiased renderer cannot allow any 
non-conservative material. If it did, it would be unable to reach a 
stable solution, because it attempts to simulate the physical system. If 
you had just one non-conservative material in real-life, the scene would 
just end up saturated with light...

So the biased renderer can handle surfaces that are perfectly 
transparent yet perfectly reflective, because it samples a limited class 
of rays that make it work. The unbiased renderer must sacrifice either 
transparency or reflectivity in order for its solution not to explode.


>   A BRDF can take light coming from several directions and calculate how
> it affects the outgoing light towards a certain direction. I don't believe
> BRDFs have the requirement that these different light amounts must be
> *averaged* instead of being added together.
> 

If you do not make an average, as more rays are traced the brightness of 
the image rises, which is not realistic. So regardless of lighting 
theory, you must do an average. It is exactly what happens in anti 
aliasing, I don't see the problem. That average, I think, stems from 
Monte-Carlo integration.

>> A black object can have a bright highlight, of course. Or rather, a 
>> bright reflection. In that case, you would lower diffuse_amount, to be 
>> able to set a higher reflection_amount.
> 
>   How is the program supposed to guess that you really wanted a lower
> diffuse amount?
> 

It does not guess, you tell it so. Because as I said, colors should be 
normalized. If you want black you have to lower the diffuse amount.

>   Besides, the black object was just an example. Take a red object, with
> a relatively high diffuse, and a white light source. The surface can have
> white highlights even though the surface is red.
> 
>   If you average the diffuse and the specular reflection, the latter
> would get a red tint.
> 

If you add them up, there will be a red tint as well. It's just that you 
clamp the components of the color after the fact, ending up with 
something white. If no clamping happens, the red tint should still be there.

-- 
Vincent

Post a reply to this message