Renderman’s Implementation of the Marschner Hair Shader

FXGuide has recently published an amazing article on the technology behind Renderman’s way of using the Marschner Hair shader.

FXGuide has recently published an amazing article on the technology behind Renderman’s implementation of the Marschner Hair shader. The article features interviews with both Professor Steve Marschner (Cornell University) and Christophe Hery (Pixar Research group).

Here is a small piece of the article to get you interested:

The success of the Marschner model is in great part due to the specular estimatation and it’s deployment of three specular lobes using multiple specular transport paths:

Primary Specular: This can be described as the specular reflection.
Secondary Specular: TRT “transmit” this becomes the colored specular contribution.
Transmit Specular: TT light transmits through the hair surface (forward scattering) and produces the important back lighting.

The key contribution of that original paper was to “identify, explain, and verify these different modes of scattering in hair and the appearance characteristics they are responsible for, as well as to provide a simple model to simulate them” commented Marschner when he spoke recently to fxguide.

The components of the original (2003 model. The first three hair examples are circular hair (1) The primary highlight) alone; (2) the TRT component (secondary highlight) alone; (3) the combined model. The 4th example (right) is the same full model showing elliptical hairs with texture due to glints.