A sunny beach. A candlelit restaurant. A creepy dungeon. In the world of moviemaking, directors increasingly use digital tools to add real and virtual characters to different kinds of backgrounds. The key to making it look realistic? Lighting. "How actors are lit is a big deal," says Paul Debevec, a computer scientist who heads the Graphics Laboratory at the University of Southern California's Institute for Creative Technologies. By creating more accurate artificial lighting on a computer, he says, his team is "giving filmmakers more flexibility" in their shots and more efficient ways to generate effects. Which means time and money saved on shooting, editing, and drawing graphics-not to mention more convincing results. An eventual goal is to create more realistic digital characters and objects that can be used in any scene. But techniques based on Debevec's work have already been used by special-effects companies in numerous feature films, including the Matrix and X-Men series. At his lab in Marina del Rey, CA, Debevec showed TR associate editor Gregory T. Huang how to use light from the real world-and algorithms from the digital one-to render an actor's face as it would appear under any conditions, anytime.