Forget dinosaurs, twisters, and giant bugs from outer space: Flubber and the digital domain were clearly meant for each other. Amorphous, malleable, and translucent, the title character in this John Hughes-scripted, Les Mayfield-directed remake of the 1961 The Absent-Minded Professor is given life entirely through computer animation. The little green bundle of energy flies, multiplies, dances, and Flubberizes inanimate objects. It's even more active than costar Robin Williams, cast as the scientist who cooks up the formula in his lab.

"We never employed any practical Flubber," says visual effects supervisor Peter Crosman. "Because of the proliferation of companies and software and technical means, it was not prohibitive to make even the fastest-flying Flubbers all digital, and all created 3D." The job of animating Flubber was farmed out to four companies, including Hammerhead Productions, Mobility, and Computer Cafe, with industry leviathan Industrial Light & Magic given the most complex task, a large-scale dance sequence.

But Williams, who spends much of the movie interacting with Flubber, was just as key a player. "We had many discussions with Robin about Flubber's look, behavior, and size, and about where to cast his eyeline," says Crosman. "But when Robin got on the set, he applied his gift for improvisation to the physics of dealing with it in his hand. We basically followed his cue as to where Flubber was and what it was doing. There's a sequence of juggling which was one of the most difficult things for Robin to mime, and also for us to fulfill; there was a lot of work in second unit [which Crosman directed] to make the chaotic movement of Flubber and Flubberized objects correspond to the physical environment."

Lighting, of course, was one of the areas that required careful attention, especially since Flubber is translucent. "We did an extremely careful job mapping out the placement and size and color temperature of every lamp," Crosman says. "We had an extensive notebook for every scene and setting, so that the creators of the computer-generated Flubber could exactly recreate the lighting in every environment. You also need all the camera information--lens, focus, even f-stop.

"All of that information had to be repeated in the computer environment, so we basically adjusted the stage in the three-dimensional CG world to exactly what we had on set," he continues. "There's clearly a key light, and there's the practical lights, but there's also the refracted lighting that comes through the back of the set. It's a very computer-intensive, calculation-intensive process, getting the environment behind Flubber to ray-trace properly through and give the full refraction to its translucence." And not only does light hit Flubber: "There's also a caustic pass, where Flubber casts its green light onto Robin's hand, almost like a stained-glass window."

This was not Crosman's only task on the project, which kept him busy for 18 months. "The thing that drew me to the production was how ambitious the film was on many levels," he says, adding that there are about 600 effects shots in Flubber. "In some ways the complexity of the flying scenes with Robin and his Thunderbird probably exceeded the complexity of dealing with Flubber," because those sequences involved combinations of full-scale, miniature, and computerized environments, with a Robin Williams puppet or "synthespian" intercut with the real thing shot against a blue screen.

In the miniature environment, Crosman says, "lighting tried to simulate the bold, single-source look of blue moonlight, and just the appropriate amount of fill to let us believe in the environment. There was a lot of work creating the sodium-vapor streetlight environment you'd find in a small rural town, and the bounce of that light off the clouds above." For the tabletop cityscape model, "you end up recapping the kind of instruments you use in the real scale. You take a 5k down to an Inkie, you use miniaturized snooting. The benefit we have in doing miniatures is we could do several passes, and segregate the sodium vapor and tungsten lighting around the homes and streets from the moonlight, which can then be digitally blended to the extent we needed."

Crosman benefited from the expertise of Dean Cundey, director of photography on such effects milestones as Who Framed Roger Rabbit, Jurassic Park, and Casper. "He provided a very consistent lighting that was entirely what we needed for doing digital effects," says Crosman. "We need a good, dense negative to work with, even in night scenes where darkness was what we would eventually get. He had the foresight to light things in a balanced manner and expose them much brighter, so we could crush them as much as eight or 10 points in post. His capabilities were a tremendous blessing."

Flubber was released in November by Walt Disney Pictures.