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Jing Li wrote:

> I did define the pigment for the object, just define it black rather than
> other color on purpose. What my understanding through reading Foley's book
> and Hill's book is that the ambient light should contribute to the final
> color of the ray even though the diffuse color of the object hit by the ray
> is black.
> 
> Please correct me.

Pov-ray ambient light use a shortcut: ambient light is everywhere, and
resulting color for the ray of light which hit/come from a surface is
independant of any angle. This is not true for the Diffuse part of the
same ray.
Now, despite being under light, black is black; in particular, ambient
black is not shiny or anything else, it's just black. Deep, and black.
Shinyness/glossiness/whatever is a coloring-model which need some
variations according some angles, so it's not possible with ambient.

The ambient global setting is the default light source spectrum.
The ambient in the finish setting is the light source spectrum to use
for that texture instead of the default one.
The resulting "ambient" light/color is as every reflected light/color:
the product of the spectrum of the incoming ray (here, the "ambient"
light source, everywhere) by the spectrum of the reflecting surface.

Your full 0.6 gets absorbed by the deep 0 black. So, it's not because it
is 0 that it does not contribute... you just do not see it.
Use a less deep black, and you might see more of its contribution.


- --
Eifersucht ist die Leidenschaft, die mit Eifer sucht, was Leiden schafft.
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