Path: utzoo!mnetor!uunet!husc6!bloom-beacon!gatech!purdue!i.cc.purdue.edu!j.cc.purdue.edu!pur-ee!iuvax!bsu-cs!cfchiesa
From: cfchiesa@bsu-cs.UUCP (Sir Xetwnk)
Newsgroups: comp.graphics
Subject: Re: silver color
Message-ID: <2029@bsu-cs.UUCP>
Date: 3 Feb 88 17:05:24 GMT
References: <2679@bloom-beacon.MIT.EDU>
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 31
Summary: In general

In article <2679@bloom-beacon.MIT.EDU>, tada@athena.mit.edu (Ivan Tadayoff) writes:
> 
> Does anyone know what values of RGB to use to make a nice looking silver?
> (as in a metallic object?)  I've tried a variety of combinations and none 
> of them seem very pleasing.
> 
> While on the subject, does anyone know a good book on how to color ray-
> tracing views?  For example, how much does a light ray change when it
> reflects off a metallic sphere?  
> 
> Thanks in advance for any help.

Without going into the math, but perhaps filling in a few general concepts,
your question isn't so much one of finding the right COLOR for "silver,"
but rather of how to vary that color properly so that it gives the impression
of a reflective, rather than dull or "matte," surface.  A silver object is
actually colorless, or perhaps "gray" (as the previous respondent's "0.95-for-
all-three-primary-colors indicates), but usually reflects its surroundings.
In general, the more clearly (less fuzzy or vague) the reflections appear,
the shinier (silverier) your object appears to be.

If I'm not mistaken, the answer to "how much does a light ray change...etc"
has to do with defining a cone whose tip is at the reflection point and whose
axis is the normal to the sphere surface at that point.  I *think* you then 
determine whether your light source is within that cone, how far (angle) it 
is from the cone axis, and use that distance to compute how much "specular"
contribution to consider at that point, to be added to the overall illumina-
tion of the surface.  The wider (larger angle-at-the-tip) the cone, the more
diffuse the specular reflection, and the softer "finish" your surface appears
to have.  As for reflecting other objects in the environment, I haven't seen
the specifics anywhere, but would think that they should be handled similarly.