Jeremy M. Praay wrote:
> I took a look, then came back later and took another look, and I would have 
> to agree with Rick.  #23 looks best to me, especially if you're looking for 
> shiny leather.
> 
> 
>>pigment { rgb 0 }
> 
> 
> I've found that I get better results when I use a very small RGB value, 
> rather than 0.  You might want to experiment with that as well.  RGB 0 can 
> look very strange when placed with other objects, in my experience.  Perhaps 
> something like "rgb <0.001, 0.001, 0.001>" or for a slightly bluish tint 
> "rgb <0.001, 0.001, 0.003>"
> 
> 
>>diffuse 1
>>reflection { .075 .15 fresnel metallic 0 }
> 
> 
> Jaime recently mentioned "diffuse + reflection = 1".  From looking at some 
> of his code, it appears that he always uses the first reflection component, 
> which would give you a diffuse of 0.925.  Not a huge difference, but it 
> might make a subtle difference.
> 
> Would the bottom (base?) of the shoe have a different specular component?
> 
> Just some thoughts.
> 
I think the diffuse component is irrelevent for rgb 0.  I think it is 
basically the product of the two values, rgb and diffuse, and the angle 
of the lightray, that are used to calculate shadow.  So if you go rgb 0 
you loose all capacity to get non-lighted shadows and instead have to 
rely on specular and/or reflection to mold the surface.  So, as you say, 
adding a little color gives "diffuse" something to work with.  The 
trouble is that just about the time that adding color starts to make a 
difference, it starts to look like grey, not black, material.

Yes I remember Jaime's suggestion too, though I thought he was talking 
about specular.  I also remember that a long time ago there were often 
threads discussing such formulas. Alas, am I now just catching up? Well 
not quite. For a long long time I typically adjusted 
diffuse/specular/reflection as some sort of loosely conceived division 
up of a unit whole.  Then it came as something of a revelation to me 
when I freed myself from that discipline.  Now, while Jaime's statement 
comes as a sobering remainder to keep it sane, I am still not convinced 
that a formulaic relationship between these elements always makes sense.

I was introducing my daughter to raytracing just the other night.  We 
were giving a sphere, with no finish specified, different colors just to 
demonstrate how the color vector worked.  I was trying to get her to 
guess how to get yellow by introducing the concept that yellow is really 
not-blue.  So first I had to demonstrate that white is <1,1,1>. We did 
the render.  "It doesn't look white, it looks grey", was her immediate 
reaction. :(

With a low rgb, radiosity also is neutralized.  So the only way to get 
any tones into the shadows is reflection. But even the slightest amount 
of reflection gives a hard-shiny look.

About the bottom of the shoe. ("Bottom" is the correct term.) Yes, if it 
was made of leather it would show wear and have tan patches.  If not, 
then it would be some homogenous material other than leather and 
therefore show different surface characteristics.  It is an important 
question because it may be true that the solution to the problem has to 
do with providing massive amounts of minute surface detail.  After all, 
shiny, homogenous, black patent leather is favored by some precisely for 
its "dark liquid", form-denying properties.

So the hunt goes on.  But I was interested to peoples reactions to gross 
adjustments of these factors across the scene in general.

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