On Thu, 11 Jan 2001 13:45:07 -0000, Tom Melly wrote:
>The trouble with ambient is that to make any real sense it should be
>influenced by the overall strength of the light-sources available. Perhaps
>one should code like this:
>
>#declare light_strength = 0.75;
>light_source{<0,0,0> color rgb<1,1,1>*light_strength translate <-300,
>300, -300>}
>object{foo finish{ambient 0.3*light_strength}}

But one does code like that, if one knows about the all-important
global_settings { ambient_light COLOR } setting.  Just look at it
as a big shadowless light source that casts light in all directions 
from everywhere.

So, the ambient setting in a finish statement seems to me as though it
should be closely related to diffuse, particularly if brilliance is low.
As brilliance goes up, ambient should go down relative to diffuse.  As
diffuse goes up, ambient should also go up.

If I were to propose a rule of thumb, I would say ambient and diffuse
should be roughly the same number, and that ambient shouldn't be included
in the requirement that filter+transmit+reflection+diffuse+specular <= 1.

The logic behind the first part is that ambient is just diffuse reflection
of light with an unspecified source, so if an object diffusely reflects
60% of any light falling on it, it should diffusely reflect 60% of the
ambient light.  (If this makes your scene too bright, turn down the ambient
light in global_settings or consider using radiosity instead of ambient
light.)

The logic behind the second part is that what an object does with light 
from unspecified sources shouldn't have any effect on what it does with 
light from a specific source.  That is, you wouldn't keep everything
below .5 just because you have two light sources, so there's no reason
to do so because you have ambient light.

Actually, now that I think about it, I'm not so sure both specular and 
reflection should be in the sum either, since the purpose of specular is 
to simulate reflection for light sources.  By the same logic, specular and
reflection should probably be fairly closely related unless you're using
blurred reflection in MegaPOV.

-- 
Ron Parker   http://www2.fwi.com/~parkerr/traces.html
My opinions.  Mine.  Not anyone else's.

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