Seeing Your Smoke and Breathing It Too

If you like the idea of hanging around smoke-filled bars, but not the reality of it, then you can thank Wojciech Jarosz for coming up with a way to see your smoke and breath it too.

In truth, animators have been able to generate images of smoke, fog, and smog for a long time. But what they couldn't do is generate those images efficiently. What Wojciech Jarosz, who is a PhD candidate at the University of California, San Diego, has done is develop techniques for creating these visual effects much faster and with much less computational overhead.

With current-generation computer graphics techniques, the computer has to compute the lighting at every point along the smoky line of sight between your eyes and, say, someone on the other side of a smoky room. The approach Jarosz, Craig Donner, Matthias Zwicker and Henrik Wann Jensen came up with -- and describe in their paper Radiance Caching for Participating Media -- uses a computational short cut called "radiance caching" to create realistic images of smoky bars and other images where some material hanging in the air interacts with the light.

With Jarosz's approach, when smoke, clouds, fog and the like vary smoothly across a scene, you can compute the lighting accurately at a small set of locations and then use that information to interpolate the lighting at nearby points. This approach, which is an extension of "irradiance caching," cuts the number of computations along the line of sight that need to be done to render an image. In addition, the radiance caching system can identify and use previously computed lighting values.

"If you want to compute all the lighting along a ray, our method saves time and computational energy by considering all the precomputed values that happen to intersect with the ray," says Jarosz. He goes on to say that "our approach can be used for rendering both still images and animations. For still images, our technique gains efficiency by re-using lighting computations across smooth regions of an image. For animations where only the camera moves, we can also re-use the cached values across time, thereby gaining even more speedup."

Posted by Jon Erickson at 01:25 PM  Permalink