Think Global, Illuminate Global

Still, there has been a lot of work done in terms of accelerating real-time rendering on graphics work stations, notes Eyal Ofek, a researcher with The Hebrew University in Jerusalem. His specialty is global illumination, in which lighting effects come from everywhere in the scene. In other words, global illumination accounts for: shadows, where one object casts a shadow on another object; reflections, where one object reflects the image of another object; refractions, the image of one object as it is seen through another transparent object; reflected lighting, or light reflected from other objects; and caustics, where light patters are reflected or refracted by the face of a liquid.

Right now, graphics accelerators can handle only local lighting effects--effects that can be calculated only by using the data of the point being rendered. Using global illumination, on the other hand, shows a 3D sphere that appears shaded, as if the light is coming from some direction, he explains. "As you can see, a great deal of lighting effects--in fact, most of them--cannot be generated using current hardware." He is working on a way to generate interactive refletions and refractions using standard graphics hardware.

"Today, work stations can render models with an impressive amount of polygons, but the visual quality of rendering has not changed much in the 20 years since its introduction," asserts Ofek. By generating global illumination effects--reflections and refractions--with hardware, the result is stunning visual quality. "The effect of global illumination on the rendered scene is drastic," he says. "The scene looks alive, with extra depth. When the effect is turned off, the scene immediately becomes dull and much less interesting."

As rendering gets more realistic, some interesting social and ethical questions arise, explains SGI's Larson. "Some people have discussed or investigated ways that computer graphics might be used to resurrect dead actors or public figures from film archives and reanimate them, making them say and do things they never said or did, and perhaps never would." While rendering can be used by forensic scientists to re-enact an automobile accident in order to show a jury that a driver had time to react and this avoid a collision, rendering could also be used to falsify evidence, Larson says. The use of rendering in this way "is already making it difficult to trust certain forms of evidence that were previously deemed irrefutable, such as photographs and video."

Larson predicts there will eventually emerge a combination of image-based and polygon rendering that will allow graphic artists to mix real-world graphics and computer-generated imagery together, seamlessly, in virtual environments.

"One of the biggest challenges from my viewpoint is creating rendering algorithms that are true to reality in measurable ways. For example, one goal in high fidelity audio reproduction is to reproduce the experience of being at a live concert. However, there are many things affecting the reproduced experience. Some of these things are easy to measure, and some are more difficult. Where we may be able to assure ourselves that the important aspects of an audio signal are appropriately preserved by the recording and playback processes, we are less able to make firm statements about such variables as the correct placement of the microphones for recording, or the speakers used for playback, or their placement in the listening room."

According to Larson, image rendering is even harder than audio reproduction. "We are not merely reproducing what we see, as in photography, but we are actually synthesizing it from more fundamental measurements and models. It's more akin to having a model for each instrument and how they are played and producing music from these models directly into a listening environment. For anyone who has heard such an attempt at an all-synthesizer concert, I think it makes it a little easier to appreciate the difficulty we face in computer graphics, for our eyes are even more discerning than our ears."