Beauty is Sub-Skin Deep – Part I

It’s been wisely said and widely believed that beauty is only skin deep. It’s debatable whether CG world was bought into the wisdom, but the skin-deep shading is no more the case these days. Beauty is certainly deeper than skin. I firmly believe that this concept has become one of many pitfalls in bringing Final Fantasy characters to life, at the time.

Human body is made of substance that scatters when the lights pass through it. Since the skin is not perfect opaque, this scattering effect should be visible and behaves depends on the skin position against the lights relative to viewing angle. For this scene I use EZ_Fast_Skin shader created by Emanuelle–a talented XSIBase member–as an alternative to the native XSI Fast_Skin Shader. It’s faster and, as suggested in the name, easier. The shader effectively calculates sub-skin scattering effects with an array of slots and parameters to simulate human skin shading.

The skin was unwrapped with RoadKill, a tiny handy free UV tool, to map three images for this object. (1)Diffuse, which was manually painted in ZBrush, (2) Normal Map, created with Z-Mapper, and (3) Specularity/Reflection map, which actually is modified normal map.

I used a single map for both reflection and specularity since those two are similar in concept. For physically-based material, specular means reflection. Reflection makes specularity of a surface, and then decays based on microscopic roughness of surface. A very sophisticated implementation of this effect is made by deploying Fresnel Law, with Index of Refraction (IOR) and viewing angle dependency. However in older materials, both specular and reflection co-exist. With this kind of material, it’s possible to have shinny material without reflection and dull material but highly reflective, which are against the physical law.

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