Halle's paper is part of the session on Image-Based Rendering.





Jensen's paper is part of the session, Rendering.


















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Rendering Adds Radiance To Every Day Life


"People are already being affected by rendering, in advertising, entertainment, and the media," explains Gregory Ward Larson, a member of the technical staff in the engineering division of Silicon Graphics. "They usually don't appreciate the effect it has on their lives, because if the rendering quality is high, it becomes transparent to the naive viewer."

"Rendering," says Larson, "is used to sell products, and to design products. It is used to evaluate the appearance of buildings and structures that may be erected later, and to visualize deteriorated artwork and ancient cities modeled from archeological records. It is used in movies, in special effects and animation, in communication, and in medicine."

Rendering will be even more meaningful in medicine when three-dimensional displays and computer screens become more widespread, Halle says. "The idea is to push 3D technologies--both the actual devices and the algorithms that generate data for them--so that they can add to the 2D display that we currently use in the operating room," Halle says. "These displays don't need glasses to be seen in 3D. The use of 3D could include 3D printouts, or holographic film, or 3D screens, such as electro-holographic displays or lenticular-sheet/LCD hybrid displays."

Right now, though, 3D images are typically printed out on a two-dimensional piece of paper, or placed on two-dimensional screens or displays. That's because most computer graphics are designed to render only a single image, just as a camera would take a photograph from a single location. Three-dimensional displays and printers, however, require many different perspectives of a single object, each taken from a slightly different position. Because this technique, multiple viewpoint rendering, uses perhaps 10,000 separate images, it takes that much longer for the computer to complete the rendering tasks. "Rendering speed is what make it practical or impractical," he notes.

Halle has come up with a new algorithm to speed up the process of multiple viewpoint rendering. It hinges upon a concept called spatio-perspective coherence. In other words, small changes in the position of the camera usually produce similar small changes in an object's appearance. Also, some of the work required to render an image can be reused for many other images, which reduces computing times, he says.

Rendering time is a major consideration for all types of rendering, particularly when it comes to photorealistic rendering, which creates images that are indistinguishable from real photographs, notes Henrik Wann Jensen, a researcher with Mental Images in Berlin, Germany. "Rendering realistic-looking images is one of the most resource-demanding sort of computations that exists," Jensen says. "Rendering the images for a film can easily require several hundred thousand hours on a single computer. I expect hardware to play a larger role, since this will allow us to render our images faster. We also may be able to improve some of the current algorithms so they can deal with very complex scenes. We need algorithms that can deal with the complexity of what we see in nature, and algorithms that can handle complicated objects."

At present, for example, its difficult, if not impossible, to make photorealistic images of large cities or outdoor environments, Jensen says. That's not an obstacle for Jensen, who is fascinated by rendering seemingly impossible images. He's developed a method to use photon maps to address the problem of rendering smoke, dust, clouds and underwater scenes. Photon maps work because the computer "does not analyze every element in the scene, but instead computes the flow of light necessary to render realistic images." Photon maps can also handle caustics, or the interference patterns made when light is focused by mirrors or glass. Examples of caustics are the light patterns on the bottom of a swimming pool, and the light pattern on a table created by a glass. Jensen notes this was an effect that was missing in "Titanic" -- there was no light reflected from wavy water or the ship, he says.


Modeling | Rendering | Animation | Interaction | Virtual Reality | Synthetic Actors