For the last few days, MTV News has been taking you inside some of the coolest aspects of "Tron Legacy," from the creative process behind Daft Punk's violins-meet-synthesizers soundtrack to the generation of the film's neon-pulsing motorcycles and warships. Now we're going to take you behind the creation of the film's single-most jaw-dropping visual effect: turning Jeff Bridges from 60-something Oscar-winner into the Bridges of 1984's "Against All Odds."

We caught up with visual-effects supervisor Eric Barba, the driving force behind the CG work on "The Curious Case of Benjamin Button," for which technicians both aged Brad Pitt into an old man and turned back time to capture the actor's 20-something look. What they managed to accomplish was nothing short of astounding, and Barba won an Oscar for his efforts.

But what Barba and director Joseph Kosinski set out to create for "Tron Legacy" was something far different — and far more challenging. "It's the hardest thing that's ever been done in visual effects," Barba explained.

See, the film stars two different versions of Bridges' character Kevin Flynn. One is the Flynn who's been trapped inside a computer-generated world for 20 years and who looks exactly like a 60-something Bridges. The other is Clu, a digital manifestation who does not age and thus still looks about 35 years old. To create Clu, Barba's team essentially had to wrap a CG mask around Bridges' face, making him look young again.

What made that task harder than the one in "Benjamin Button" was that, for "Tron," Barba had to do everything in 3-D. "What scared us with Jeff was that we're at the beginning of this technology," he said. "People were very happy with the way Benjamin came across. But there's leeway because we've never seen Brad Pitt as an old man. This was 10 times harder. We all know what Jeff Bridges looks like at 35. Right off the bat, we were setting ourselves up for other people's expectations."

To begin, the filmmakers brought in makeup-effects master Rick Baker ("Men in Black") to build a likeness of a young Bridges' head that would serve as a basis for their CG work. But that likeness soon had to be thrown away, after filmmakers decided they wanted an even younger version of the actor. There was no time to build another head, so Barba's team had to re-sculpt everything in the computer. Then in came Bridges himself.

"We had to derive the face from Jeff's performance, so we built this four-camera, head-mounted system that Jeff would wear on set with the other actors," Barba said. "We'd take the data from those four cameras and triangulate each point and get a floating, 3-D point cloud of his face. We ran that through sophisticated software we wrote and it rebuilt his performance on the younger visage."

Yet that was just the beginning. The effects team also had to mirror the particular movements of Bridges' face — muscles, skin, expressions and the like — so that the CG face would approach a photo-realistic representation rather than dipping into the much-dreaded "uncanny valley" in which CG creations fail to look appropriately human.

Early viewers have been split over the success of Clu: Some have applauded the work, while others have argued the character has not escaped that digital valley. The filmmakers knew exactly what they were getting themselves into when they started out, and Barba remains ecstatic over what they were able to accomplish.

"We knew Clu would be a much, much more difficult challenge then Benjamin," he said. "But hey, someone's got to take those chances and those risks and go for it. We thought this was a great project to do that."

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