MacDirectory Magazine

Asia Ladowska

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Caustics are among the most beautiful lighting phenomena in nature. Caustics are formed as light refracts through or reflects off specular surfaces. Examples include the light focusing through a glass of cognac, the shimmering light at the bottom of a swimming pool, and even the beams of light from windows into a dusty environment. Caustics History I have been fascinated by caustics for a long time. My career in computer graphics got started after attending a keynote by Peter Shirley (at the time a visiting professor at Cornell University), who said we do not know how to render caustics except in simple scenes such as caustics on a diffuse plane. I was a student at the time and I had been working on an algorithm called photon mapping for fun that did exactly what he was talking about. I did not think it would be useful at the time, but his keynote made me think otherwise, and I started publishing papers with a focus on rendering caustics [1]. My caustics scene of choice at the time was a glass of cognac as shown in figure 1. A few years later I worked with Per Christensen at mental images, and we extended photon mapping to render volume caustics as shown in figure 2. Photon mapping works by tracing photons from the light sources into the scene and storing these photons as they interact with the surfaces or volumes in the scene. The second step is rendering the scene using a ray tracing (or path tracing) algorithm that uses the photons to compute caustics and other lighting elements. The original photon mapping algorithm can render beautiful caustics and global illumination, but it is limited to the number of photons that can be used to render a given scene. I worked together with my PhD student at UC San Diego, Toshiya Hachisuka, to overcome this limitation and it led to the development of progressive photon mapping [2].

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