Improved normal distribution function for skin specular reflection rendering based on GGX distribution

Abstract

With the development of subsurface scattering technology in recent years, skin rendering has also increased realism. However, as an important part of skin rendering, specular rendering now mostly still uses the K/S model based on Beckmann’s normal distribution function, which makes skin specular reflection always too concentrated, reducing the realism of rendering. To solve this problem, this paper proposes an improved normal distribution function: GGX-Improved based on the GGX normal distribution function. By introducing a parameter K into the GGX normal distribution function, it can realize the adjustment of the tail length of the K/S model specular reflection while ensuring the shape invariance, to make the skin specular reflection softer and more natural, which enhances the realism of the skin rendering.