[jfrancis]

In his skin tone tutorial, Steven Stahlberg calls it "warming up the terminator"

"So we need to make the nightside warmer, and the dayside cooler. Also, from observing real skin, we can see that the terminator needs to be even warmer than the nightside."

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Prometheus|ANJ refers to it here: http://www.itchstudios.com/psg/tuts/middle.jpg

"If you paint everything with the same hue and saturation it will look boring. "

http://www.itchstudios.com/psg/art_tut.htm

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I have a suggestion for how to better address these issues in Maya.



"The typical CG light only loses luminosity as it rolls off from direct to oblique illumination. That can look dull.

Here's a technique for introducing angle-based hue falloff into the light for a richer look."

http://www.digitalartform.com/archives/2005/08/hue_falloff_in.html

The idea is to calculate the "facing ratio" not of the camera's view of an object, but of the light's view of the object, and to map that light facing ratio through a ramp and back into the light's color attribute.

It's not new to CG, but it is hard to do in Maya.

[Steven Stahlberg]

This way works through the light, but if you want to make a skin shader you need to work the same effect into the shader, able to respond to any lights... this is what I did in my tutorial, if you check it a bit further down, there's a tiny little network - a Lambert, a clamp and a ramp - that changes the color of any of the shader's attributes you choose, to any color based on the light angle.

Here's an image that maybe explains it a little better:



edit:
(Note that in my original tutorial I forgot to mention you have to change the value ringed in red from default zero to 1, sorry everyone)

[jfrancis]

The idea of using it for skin came more as an afterthought. That's why the objects are all cyan/blue, and not skin-toned.

I was mainly going after the Prometheus idea of having the light change hue and/or saturation

It's an unusual approach, to make the lights behave like this.

Do you think this kind of thing should be confined to the surface shaders, and not the lights?

[Steven Stahlberg]

Yes it is an unusual approach, which is good. No, the effect doesn't have to be confined to the surface shaders. Most commonly, an artist would probably prefer to control the effect on a per-object basis, but the more tools in the toolbox the better.