conducters' highlights vs dielectrices' highlights

#1

when reading the thread “the science of cg”,I come up with a problem.
http://forums.cgsociety.org/showthread.php?f=21&t=650761&page=1&pp=15

Assume that a dielectric object is pure red,which is litted by a pure white light(or even more white).Then its highlight would be pure white.

But if the object is a conducter or metal,the highlight’s color should be pure red.

According to the thread above,this is because of light reflect on the surface of metal,but subsurface of dielectric.

In my view,when a gold is gold,not the highlight is gold but all surface looks gold.What means all the light comes to the surface of the metal then reflect in a color,not only the highlight part.

From some pictures,I found that the metal’s highlight always don’t have color,but appears white.

For dielectric have no specular reflection,only have diffuse or subsurface reflection,and the subsurface absorb some colors and reflect others.Obviously,highlight is part of the reflected light and why the highlight is white.Shouldn’t it be colored?

otherwise,in our daily life,metal’s highlight often apears to be white,and why.

A big guess about these:maybe the dielectric’s highlight is not pure white,but a color at (280,270,270),but we could not recognize and that “looks” white.And this is suitable for conductors.

The highlight turns to be a highlight is just because of the value is above(255,255,255) I think.

So the color get less saturated and the value get brighter,and result in a white.

This is just some thoughts,if I were wrong,please put me right.

Hope I express clear,and expect real discussion.

#2

You’re basically correct. Be careful about the way you’re thinking about things though:

In my view,when a gold is gold,not the highlight is gold but all surface looks gold.What means all the light comes to the surface of the metal then reflect in a color,not only the highlight part.

A highlight is simply a reflection of something bright (most often a lightsource). The gold surface does not care where the light came from, it only “knows” to reflect light in one way - as gold. As you say, highlights from metallic surfaces will often appear white because they are brighter than can be represented in a computer image.

(Side note - This is also to do with “white points” - both of the capture device, and of your eye. But that’s a much longer topic).

Dielectric reflections are not pure white, but are close enough that we can represent them as such.

#3

thanks for your reply.I’m really not sure whether I’m right,just some guess,and I’m looking for some papers or threads to read.

If you got some to share,that’ll be thankful!

#4

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