Bill Desowitz finishes our series on the computer-generated effects of Star Wars Episode II. This time he goes behind the motion-capture process to discover the challenges of creating a clone army.
Apparently there was a whole other behind-the-scenes battle going on between the clones and the droids in Star Wars Episode II: Attack of the Clones -- the battle over motion-capture complexity. The clones won that one, too, given the extraordinary demands of these goose-stepping warriors that, unlike the droids, aren't supposed to look computer-generated.
The Problem With Clones...
"The battle droids involved pretty routine cycles, but we wanted a dead-on live-action, second unit style of shooting for the clones," explains Jeff Light, Industrial Light & Magic's motion-capture supervisor. The training sequence in which we are first introduced to the clones in Episode II took seven weeks to animate. Here the clones put on their helmets, march in formation and snap to attention. It was actually more demanding than the thrilling arena battle sequence, according to Light. "There were different orderly groups interacting during the formation session. It was a real organizational challenge.
"For every take in motion-capture, Sylvia Wong [the animation lead] would find an extra human move or would hand adjust to animate on top of the performance. But we were careful not to change a performance with keyframe animation. If the performance had to be changed, we would do another session."
Working with Wong, Light would get the motion-capture performance he needed in the studio and then deliver data as a moving cloud of points. "I had a team apply data to the characters," Light says. "After tweaking the performance, data was fit into a library and then the translation rotation was run through space, which Sylvia placed along a path."
The realistic look of the clones was achieved as a result of advances in the Vicon 8 optical motion-capture system (previously used in Episode 1) and an improved pipeline for ILM. The 20-camera high-res set-up (as opposed to the earlier 7-camera low-res set-up) provided more bit depth, which allowed the animators to cover every angle in real-time to see how a person relates to his environment.
"There have been a lot of advances in motion-capture," Light adds. "It's a lot faster and more sophisticated -- you can visualize much better and dial a performance based on mood more exactly."
This occurred, for instance, when George Lucas instructed them to dial a much harder snap. Interestingly, James Tooley, the technical animation lead with a military background, suggested a stylized, Gestapo-like move that Lucas approved.
"I played a clone during one of the motion-capture sessions, which was later replicated 100 times, so you could say that they cloned me," Tooley jokes. "The labeling and triangulating trajectories of motion-capture points were better in Episode II, which meant the volume of work was more efficient."
Taking an action stance! James Tooley strikes a pose. Photo credit: David Owen. The realism of the clones was a result of Vicon's new mo-cap system and ILM's improved pipeline. Photo credit: David Owen.
Light says they did between 100 and 150 takes a day since they didn't require real-time synchronization. That's because their motion-capture needs didn't revolve around one or two primary performances, as in the two Mummy movies they recently completed.
Tooley says one of the most challenging moments was when the clones pick up their helmets during the training session. This required a CG head to be modeled using a combination of Maya and Isculpt, with rendering done using Renderman and Mental Ray.
The droids had their challenges too. While they were required to fire in a straight line in Episode I, here they were asked to fire up more, since the clones were dropped into the arena. Meanwhile, rigid body dynamics was used to "slice" the droids during the battle.
Animatics, which were designed by Lucas and his team, were very specific, of course, about the placement and timing of moves during the battle sequence. Light says the battle just hummed along: "When the clones pile out and fire at the droids, I was directed in a suit that day," he admits. "There was lots of jumping on and off transports and striking dramatic poses while firing at the droids. I came to a fast stop, landed and recoiled with my knees standing on a platform. You act like you're coming to a stop as if you're in an elevator. At first, I thought we'd have to build a rig -- but no."
And there were retakes, such as when Padme and the clone trooper roll down a hill during the battle before interacting. "There were two separate shots after one long shot, and George didn't like the performance," Light recalls. "It was too tough for cleanup work, so we went back and moved into a new performance and blended the two performances. This time out we had higher quality data with less cleanup and a faster pipeline. It was a major improvement in cleanup data. We went from a crew of six in Episode 1 to just one person, Alex Frazao, in Episode II."
Fortunately for Light, he had shot enough variations to mix and match throughout Episode II. "I've got a sixth sense about what George might want to do," Light adds. "You can't shoot every variation. Yet it's not enough to shoot only what you're assigned to do. With CG, every little move is scrutinized like in live-action."
Bill Desowitz is the former editor and managing editor of Animation Magazine, and writes about film regularly for the Los Angeles Times and the New York Times.