Graphics Reference
In-Depth Information
1
IV
Realistic Real-Time Skin
Rendering on Mobile
Renaldas Zioma and Ole Ciliox
1.1 Introduction
Rendering realistic human skin has always been a challenge. Skin and especially
faces have many subtle properties to which our brain and eyes are very well
adapted. As observers we are very quick to spot discrepancies and missing details
in shading of the skin—and reject them as implausible.
Despite these challenges, the task of rendering realistic skin in real time has
became possible in recent years [Jimenez 12] using the power of modern GPUs
and physically based shading models. In this chapter we will discuss how to adopt
the most visually important aspects of skin shading—this time on mobile GPUs.
1.2 Overview
The challenge of skin rendering lies in the fact that both aspects of light reflectance—
(a) subsurface scattering and (b) surface reflectance—are more complex compared
to most non-organic materials like plastic or wood.
For many uniform materials [Pharr and Humphreys 04] we can approximate
subsurface scattering computation with a single diffuse term and surface re-
flectance with a simple calculation of specular—using Blinn-Phong, for example.
Skin, however, consists of multiple layers of translucent tissue with different
light reflectance and scattering properties. In order to achieve a plausible image
at real time, we have to find an effective approximation of light interacting within
multiple tissue layers.
1.2.1 Skin Surface Reflectance Model
When the light hits the surface of the skin, a small fraction of it is reflected
from the outermost oily layer. The oil and tissue cells of the outermost layer are
