Illuminating Global Illumination
The ubiquitous impact of global illumination is undeniable: Everything looks richer, warmer and more natural. Indeed, at the Sci-Tech Awards dinner on Feb. 12 at the Beverly Wilshire Hotel, Eric Tabellion and Arnauld Lamorlette will receive Academy certificates of Technical Achievement for pioneering a production solution on Shrek 2. Lamorlette tells us all about the global illumination breakthrough, having spent eight years at PDI/DreamWorks after co-founding Buf Compagnie. He is currently CTO of the new technology company, The Bakery.
Bill Desowitz: What was your global illumination solution?
Arnauld Lamorlette: What happened is at the end of Shrek, before it was released, we had a lot of people on the payroll [at PDI] and had to use them. And there was no project. The thing is: we did some tests on The Matrix Reloaded. At the time we were considering doing effects potentially for [the two sequels] to do that as a bundle, and they wanted us to prove that we could deliver a photorealistic look. So during these tests, Eric Tabellion personally at home he developed a photon mapping global illumination approach, which was good but is slow and not usable in production. But here it was more for effects. So we did the test and at the same time at PDI/DreamWorks we developed a technique for subsurface scattering, which got an Academy Award, too, baking the first illumination in point clouds. This improved a lot the speed of subsurface scattering. So we thought of baking the first illumination in point clouds instead of using photons for global illumination. And then evaluate the point clouds to compute the global illumination. Basically, it's what most of the people are doing on the market today. Because we use point clouds, you have a very regular distribution and control and so you have something more stable and faster.
The second step was that since PDI was using proprietary nurbs surface (which have natural biometric UVs), so we could use textures instead of particles to record the first direct illumination. And the nice thing with textures is you can mip map them, and the whole production pipeline was designed for textures. We already had the software, interpolation and mip mapping and filtering. And because PDI was using nurbs instead of polygons, it was possible.
So we switched to textures and things got faster and we had a very natural way of filtering images and direct illumination. On top of that, there was the work technique, which is called irradiance caching, that we did a lot of improvement on. We found criteria that were faster and the fact that PDI/DreamWorks already had the ability to allow a two-pass approach.