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>From atc@ut-sally.UUCP Tue Feb  2 01:03:33 1988
Path: leah!uwmcsd1!ig!agate!ucbvax!husc6!ut-sally!atc
From: atc@ut-sally.UUCP (Alvin T. Campbell III)
Newsgroups: comp.graphics
Subject: Re: silver color
Message-ID: <10287@ut-sally.UUCP>
Date: 2 Feb 88 06:03:33 GMT
References: <2679@bloom-beacon.MIT.EDU>
Reply-To: atc@ut-sally.UUCP (Alvin T. Campbell III)
Organization: U. Texas CS Dept., Austin, Texas
Lines: 55

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.

	You are attempting to do something very difficult.  Metallic
reflection can not be done very accurately using only an RGB triple 
to model reflective properties.	

	The most common shading model in graphics, developed at the
University of Utah, assumes that the diffuse color is dependent on the
light source color and the object color, but the specular color
is dependent only upon the light color.  This is a reasonable
approximation for plastic, but not for metal.  Most of the perceived
color of metal is from a specular component dependent on the light
and the surface properties.

	A reference which gives a starting point on how to do metallic
shading is the following:

	Cook, Robert L., and Kenneth E. Torrance, "A Reflectance Model
	for Computer Graphics", Computer Graphics (Proceedings of
	SIGGRAPH '81) v. 15, no. 3, (August 1981), pp.307-316.

	After digesting the material in the above reference, which will
probably take a while, you can get reflectance spectra from 

	Purdue University, Thermophysical Properties of Matter,
	v. 7: Thermal Radiative Properties of Metals, 1970.

	If all of this seems like too much work, and you just want to
settle for an RGB triple for silver, the best you can do is probably
the following:

	R = .95   G = .95   B = .95 
	Diffuse Coefficient = .25
	Specular Coefficient = .75
	Specular Power = 6.0

	I hope this helps.

				--A. T. Campbell--
				Computer Graphics Lab
			    Department of Computer Sciences
				University of Texas
				   Austin, Texas
				atc@sally.CS.UTEXAS.EDU