Hanrahan himself was a founding employee at Pixar Animation Studios from 1986 to 1989 and was a part of the design team on the original RenderMan Interface Specification and language. Their technique for Sub-Surface Scattering (SSS) has been used by renderers such as Mental Ray or V-Ray worldwide. For example, Jensen was awarded an Academy Award in 2004 together with Marschner and Hanrahan for ‘ pioneering research in simulating subsurface scattering of light in translucent materials’ as presented in their paper “A Practical Model for Subsurface Light Transport.”. This was quite the research group, each member is a towering figure in CG. The 2003 paper was co-authored with Steve Marschner by Henrik Wann Jensen, Mike Cammarano, Steve Worley, and Pat Hanrahan. “When I moved to Stanford I found that Pat and Henrik were independently also looking at the same papers-so we knew we had to pursue it! We did the first part of the work (including the measurements that supported the paper) while I was at Stanford, and finished up the paper after I moved to Cornell” he comments referring to several of his co-authors. Lengyel thought someone who cared about reflectance and scattering ought to take a look and import them to high end graphics, and this got Marschner interested in Hair for the first time. “My interest in hair scattering started while I was at Microsoft and Jed Lengyel (a former lab-mate of mine at Cornell) showed me some cosmetic chemistry papers he had come across while working on a real-time hair rendering system” explained Marschner. The 4th example (right) is the same full model showing elliptical hairs with texture due to glints. 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 components of the original (2003 model. 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. Transmit Specular: TT light transmits through the hair surface (forward scattering) and produces the important back lighting.Secondary Specular: TRT “transmit” this becomes the colored specular contribution.Primary Specular: This can be described as the specular reflection.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: We spoke to both Professor Steve Marschner at Cornell University and Christophe Hery at Pixar Research group about the evolution of Pixar’s PxrMarschnerHair solution. The primary Marschner model has been optimised and extended by the Pixar Rendering Research Group from the initial paper published in 2003 by Steve Marschner et al : Light Scattering from Human Hair Fibers. (Model and Groom by TELYUKA created with Maya, Shave and a Haircut, & RenderMan (see also our Saya story on Telyuka)). The advanced hair model is innovative for its complex backscattering and glint and when it was released in RenderMan 19, it was the only commercial renderer that offered those features. The Marschner Hair shader was first released in RenderMan 19 and it has been improved for the newest release 21.5. Believable hair adds not only realism but production value and key character personality. This remarkable work has been both significant and enormously impactful. A major milestone in RenderMan’s hair solution was the addition and subsequent update of the Marschner Hair shader. Hair is a key factor in so much of Pixar’s character work. Pixar has long needed to be able to produce CG hair for film’s such as Monsters University, Good Dinosaur, Finding Dory (the seals) and many others. Good Dinosaur was the first use of PxrMarschnerHair, but with RSL (since it was the last film rendered using Reyes), Finding Dory was fully rendered with the RIS hair implementation in RenderMan. Monsters used the older simplified hair shader, but it was one of the first uses of importance sampling for some of Marschner’s model terms.
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