Vincent Le Chevalier <gal### [at] libertyallsurfspamfr> wrote:
> >   Unless I have understood something completely incorrectly, I think that
> > "unbiased rendering" simply means that light is not assumed to be coming
> > from a specific direction, but the entire space is sampled for possible
> > incoming light.
> > 

> But that means that the images should be different, no? And I mean, more 
> than just noisy...

  It means that the scene has global illumination. It doesn't make surfaces
more opaque.

> >   (Besides, I think the only difference pure unbiased rendering would do
> > is to make the image have global illumination, ie. what povray calls
> > "radiosity", especially if big area lights are used instead of point
> > lights.)
> > 

> Well that's a big difference

  Not that much of a difference. It doesn't make surfaces more opaque,
for instance.

>, and I don't know if it's really possible 
> or even desirable to make a single path if you're not looking for an 
> unbiased result.

  I don't believe unbiasing makes surfaces more opaque, so I don't see
how that is any relelvant.

> I was thinking more of your reflection 1 transmit 1 example. Energy 
> conservation is still one of the basic properties of BRDFs. There is no 
> way you can represent that with a BRDF. Of course all BRDFs are only 
> approximations, but that does not mean that they do not have 
> constraints. I guess my use of "physically accurate" is the problem here...

  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.

> 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?

  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.

-- 
                                                          - Warp

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