This could be the single biggest hurdle in realistic cg since Gouraud shading… as for me, I’ve been wrestling with this since -95. Like many others, I’ve been extremely frustrated by it, mainly cause until about -00 very few knew much about it, and no one could answer my questions. So -99 I found my own home-made method, a pragmatic approach that sidesteps simulation. (When we have the software and the power to do nice simulating, of course we should, but until then this kind of ‘kludgy’ approach might serve ok.) My terminology is astronomy-based, because it’s clearer and more concise: Dayside = where light hits Nightside = where light doesn’t reach Terminator = the transitional zone between night and day
Disclaimer: I mention Maya a few times, because that’s what I use, but very similar effects can be achieved in any other highend 3d software.Pardon the crappy geometry, but I had to rapidly make big changes to the original face due to unforeseen copyright issues – sorry. Of course, to improve a skin shader you need to look at the real thing, I’ve found the best references are here.
Faking Translucency[You must be registered and logged in to see this image.]
Starting from the beginning – as we all know, if you use a plain Lambert and put a skin-colored texture in the color channel, you end up with something like this: the “Copper Zombie”. We see it in many beginner’s work, and still today in game graphics, since they often use quite simple shading. The skin is a horrible dead greenish-gray in the shadows, and a metallic orange in the highlights – a bit like a corpse touched up with copper-tinted makeup.
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. (Warmer in this case means more orange/red, and cooler means more blue.)
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My first efforts used the ambient or incandescency channels to create some Global Warming – making the whole head redder. I sometimes even tried making the color channel and spec channels bluish. But this is of limited usefulness – when you get the terminator as warm as it must be, the nightside is too red, and the dayside too bright.
So leave the ambient like this, maximum saturation but a fairly low value. It’s ok, better than the corpse, but still not very realistic. [You must be registered and logged in to see this image.]









Here’s where it gets fun. Take a cartoon-shader – doesn’t matter which one, as long as it can give you simple control over which color ends up where, and you can get rid of the sharp edges between the colors. (We’re not going to use any outline function, just the flat-shading function… except not flat.) The shader I use here takes its color info from a ramp (in Maya, just switch the interpolation to ‘linear’ or ’smooth’ instead of ‘none’). The original cartoon]