Dual Scattering for Hair

Dual scattering offers an extremely fast simulation of multiple scattering in hair. No parameter tweaking is necessary to achieve accurate results with arbitrary lighting conditions. In this figure, the path tracing reference takes several hours to compute, while by using dual scattering we can reduce this time to several minutes in our offline implementation or even real-time frame rates with our GPU implementation, which uses a similar approach to Deep Opacity Maps. At the bottom row we see the results of single scattering only and existing non-physical techniques that require significant parameter tweaking, which still fail to achieve the accuracy of dual scattering as compared to the path tracing reference. Click on the image to enlarge.


When rendering light colored hair, multiple fiber scattering is essential for the right perception of the overall hair color. In this context we present a novel technique to efficiently approximate multiple fiber scattering for a full head of human hair or a similar fiber based geometry. In contrast to previous ad-hoc approaches our method relies on the physically accurate concept of the Bidirectional Scattering Distribution Functions and gives physically plausible results. We show that the complex scattering effects can be approximated very well by using aggressive simplifications based on this theoretical model. When compared to unbiased Monte-Carlo path tracing, our approximations still preserve photo-realism in most settings but with rendering times at least two-orders of magnitude lower. Time and space complexity are much lower compared to photon mapping-based techniques and we can even achieve realistic results in real-time on a standard PC with consumer graphics hardware.

See also Hair Modeling at University of Bonn.


A complicated hair model
A complicated hair model illuminated by two light sources, comparing offline and real-time implementations of Dual Scattering to Path Tracing reference result.


This is SIGGRAPH2008 Computer Animation Festival video of Dual Scattering. All frames are captured in real-time on a GeForce 8800 GTX graphics card.
Download video (avi): [High 3.54 MB] (Requires xvid codec.)

An interactive session with changing light and hair properties. This is SIGGRAPH2008 paper video of Dual Scattering. All frames are captured in real-time on a GeForce 8800 GTX graphics card. The average frame rate is about 14 fps.
Download video (avi): [High 1.73 MB] (Requires xvid codec.)


Arno Zinke, Cem Yuksel, Andreas Weber, John KeyserDual Scattering Approximation for Fast Multiple Scattering in HairACM Transactions on Graphics (Proceedings of SIGGRAPH 2008), 27, 3, 2008