attack of the clones - 6/02

The first of a two-part series

By Barbara Robertson

All images © Lucasfilm Ltd. & TM. All Rights Reserved. Digital Work by Industrial Light & Magic.

Visual effects and Star Wars have been hand in glove since George Lucas founded Industrial Light & Magic a long time ago to create galaxies far, far away. Each of the Star Wars episodes, starting with the first in 1977, has pushed the state of the art of visual effects and filmmaking, and Episode II is no exception: All but 161 shots in the film are visual effects shots. Indeed, it would be difficult to find another film in which visual effects and, in particular, computer graphics, were woven into the fabric of a film with as much persistence as in Episode II -unless it were Episode I.

Episode I, released in 1999, demonstrated ways in which visual effects can drive a new method of filmmaking. Under Lucas's direction 2D, 3D, and live-action elements were pieced together for this film like a many-layered jigsaw puzzle to create intricate fantasy scenes and locations. Most of the film was made from a combination of 3D set extensions, virtual environments, 2D elements, and 3D characters mixed with live-action footage. It was an extraordinarily ambitious effort: Of 2200 shots in Episode I, 1900 were visual effects shots. (See May, June, and July, 1999.)

When the clones were in uniform, as at right, they were always digital. Animators at Industrial Light & Magic created the clones' performances starting with data captured from Vicon's optical motion capture system and with proprietary and House of Moves'

The same is true of Episode II...and more.

Bigger and Better
Episode I showed that a new type of filmmaking was possible. Now with Episode II, ILM shows what it learned while making Episode I and during the three years hence.

Set 10 years after Episode I, the story begins with an assassination attempt on now-Senator Padmé Amidala (actress Nata lie Portman), which causes the Jedi Council to send Jedi Knight Obi-Wan Kenobi (Ewan McGregor) and his apprentice Anakin Sky walker (Hayden Christensen) to investigate. Obi-Wan discovers a clone army being man u factured for the Jedi and uncovers a separatist movement led by former Jedi Count Dooku (Christopher Lee) that threatens the Republic. Meanwhile, a forbidden romance develops between Anakin and Padmé.

ILM created 2817 shots for this film, of which 2000 were used, and those numbers tell only part of the story. "We had more shots [than Episode I] and most of the shots are more complex," says John Knoll, visual effects supervisor on both films. "We have more digital characters in the shots, more digital environments, and the shots themselves are more technically challenging in that more of them have big camera moves." In Episode 1, the camera was in a fixed location 85 percent of the time. In Episode II, it moved 85 percent of the time.

For a shot such as this to seem plausible, Jar Jar and Yoda's digital clothing needed to look realistic. From left to right: Mace Windu (Samuel L. Jackson), Senator Bail Organa (Jimmy Smits), Jar Jar, Padmé (Natalie Portman), Dormé (Ros

As with Episode I, ILM divided the work into three units. Knoll's unit created a speeder chase through Coruscant's skyscrapers, a diner scene, the space battle inside the Geonosis asteroid belt, arena sequences in the clone war, and a short scene with the character Watto on Tattoine. Pablo Helman supervised most of the shots on Tattoine and Naboo, and all the shots on Kamino, which Knoll calls the "perfect storm" planet. Dennis Muren and Ben Snow supervised droid factory shots on Geonosis and huge ground battle scenes in the clone war. In addition to the effects supervisors, Rob Coleman returned as animation director, this time in charge of "everything that moves."

CG Characters
Episode II has 70 minutes of animation, 10 minutes more than Episode I and nearly as much as an animated feature. Sixty animators worked under Coleman's supervision, compared to 45 for Episode I, and they created 30 percent more characters.

CG characters returning from Episode I include Jar Jar (briefly), now a Senator, Watto, and the droids. Also, a Sebulba-like character can be seen in a speeder and slipping out the door of Dexter Jettster's diner. Dexter himself is a new CG character, four-armed, sloppily dressed, and an old friend of Obi-Wan. The CG Poggle the Lesser, on the other hand, a nasty, insect-like Geonosian, is on the dark side with Count Dooku, as are the new CG characters Shu Mai, San Hill, and Wat Tambor. The jury is out on the long-necked, ethereal, CG Kaminoans Taun We and Lama Su, who are manufacturing the clone army.

Shu Mai: lives on the dark side

The clones, replicas of bounty hunter Jango Fett (Temeura Morrison), are real and not real. When they're out of uniform, ILM replicated Morrison's image. When in uniform, they're digital. "They look like storm troopers," says Coleman, "but they were all 100 percent CG. There were no people in suits." In addition to humanoid characters, the crew created creatures, with the three monsters that attack Padmé, Anakin, and Obi-Wan in the arena having the biggest scenes.

San Hill: banking clan chairman

Of all the CG characters created for Episode II, though, the most important was Yoda, who appears in 127 shots. "That's the reason I did the movie," Coleman says. "To do Yoda. George [Lucas] felt that my team was coming along nicely in Episode I, but there was always the sense of, well, could you really handle someone like Yoda?"

Wat Tambor: techno union foreman

To answer the question, Coleman and modeling supervisor Geoff Campbell recreated six shots out of The Empire Strikes Back (1980) with a CG Yoda. Those shots convinced Lucas to give them a go-ahead to create an entirely digital Yoda.

Geonosian: insect-like and nasty

Campbell started working in ILM's I-Sculpt with scanned data from a maquette of Yoda's head. "One thing that I try to push for with my modelers is to not just work on the surface stuff," Campbell says. "They need to get in there and really work on the inside of the mouth, give a thickness and shape to the tongue, the lips, and the wall of the inside of the cheek." For Yoda's clothes and body, modelers worked in I-Sculpt, Alias|Wavefront's Power Ani mator and Maya, and Avid's Softimage 3D. Once Yoda was underway, more modelers joined the team and began to sculpt the other CG characters, monsters, and digital doubles, eventually resulting in some 66 characters, 12 of which speak.

For facial animation, ILM uses shape blending. Thus, for example, to create Yoda's face and prepare it for animation, Campbell sculpted hundreds of shapes based on his understanding of anatomy and underlying muscles. One shape might control Yoda's tongue, another the corner of his eye. "We have procedural systems for bodies, but when you get into the subtleties of facial performance, it's all about the final look, not about whether it's correct," Campbell says.

Fight, Yoda Does
For Yoda, who had once been a puppet, reining in computer graphics possibilities became a delicate balancing act. If the modelers and animators went too far in one direction, Yoda looked like a little green talking man. In fact, when Frank Oz saw the early tests, Coleman says he believed Yoda's face was over-articulated-the original puppet didn't do much more than open and close its mouth when Yoda talked. "But, when we created a frame-accurate version of Yoda, matching him to shots from Empire, people said it didn't look like the puppet at all," Coleman says. "People have a memory of what they thought they saw Yoda doing. They projected a personality onto the puppet." Thus, the digital Yoda's facial expressions had to match expressions people thought they saw on the puppet.

In addition to Cole man, three lead animators, Tim Harrington, Linda Bel, and Jamy Whe less, were responsible for Yoda. Together, they convinced Oz, too, that Yoda could be digital. When Oz recorded Yoda's final dialog and saw the final animation, he sent Coleman a congratulatory letter and thanked him for staying true to Yoda's character.

Kaminoans Lama Su (left) and Taun We (right) tell Obi-Wan (Ewan McGregor) about the clone army. The Kaminoans' clothes were modeled in Maya and animated with ILM's proprietary cloth engine.

One way the team helped keep digital Yoda in synch with his earlier puppet self was to replicate accidental ear bounces and other jiggles that happened when the rubber puppet moved. What they could not imitate was the puppet walking around. It didn't, except for two shots in Episode I. "George really wanted to get him up and moving around and, in one case, fighting." says Coleman. And fight, Yoda does.

In Episode II, Yoda was always a digital character rather than a rubber puppet, which allowed the Jedi to make more masterful moves.

In that sequence, Count Dooku has already wiped out Obi-Wan and Anakin. Yoda hobbles into the scene, puts down his cane, gives Count Dooku a "You want to play with me?" look, and be comes the fastest, cleverest Jedi warrior yet as he jumps, spins, and slashes at Dooku with a light saber. When the fight is over, Yoda picks up his cane and walks out like a little old man. "This [sequence] sums up for me where I wanted to go with the character," says Coleman. "You could not do that with a puppet."

Digital Stunt Doubles
Jedi stunts also prompted Lucas to ask ILM to create digital doubles. "When you do live-action stunts, there's an artificial style of cinematography and editing that's imposed on you," says Knoll. "George wanted to shoot and edit stunts in the same style as the rest of the movie. That meant we had to go from live-action actors to CG and back in the same shot."

Coleman pulls an example onto his screen to demonstrate: a fight scene between Obi-Wan and Jango Fett on a rooftop in the rain. Sometimes Obi-Wan and Jango are actors or stunt doubles; sometimes they're digital. It's impossible to tell. As the scene plays on his monitor, Coleman speaks as rapidly as he can while pointing to the moving characters on his much-fingerprinted screen, "They're both real, everything else is CG. He is real, nothing else. He's CG. Only Obi-Wan is real. Everyone is CG. Everything is CG. He's CG. He's real. He's CG. He's real. He's real. That's CG. That's CG. That's all real. He's CG, he's CG, he's CG. That's CG water."

To give animators tools for creating Yoda's facial expressions, modelers sculpted hundreds of shapes in ILM's I-Sculpt software that could be blended by animators using the studio's Caricature software. Yoda's body was modeled in I-Sculpt,

What They Wear
A big factor in making this shot work was the cloth simulation, which had to allow match cuts from CG cloth to real cloth. "It's a lot more difficult than doing clothing in an all-digital feature because in those, the audience never has a frame of reference," says Coleman. Also difficult was putting Yoda in his digital robe next to other Jedi in their real robes.

The basic cloth simulation engine, which runs within ILM's proprietary Caricature software, was first used for Episode I, according to Ari Rapkin, CG software engineer. For Episode II, the R&D team added new algorithms for friction. "Previously, cloth would just collide with objects," she explains. "Now, there's temporary sticking until the collision object moves away fast enough or strongly enough for the cloth to let go."

By setting parameters in Caricature, ILM's simulation team defined how cloth moved-alone, in collisions, and in interactions with the environment.

This was important for a shot in which CG Dexter greets real Obi-Wan. They're in the diner; Obi-Wan has his back to the camera. When Dexter's digital arms reach around Obi-Wan to give him a hug, we see his CG hands affectionately rumple the Jedi's robe. To make that bit of magic possible, when Dexter hugged Obi-Wan, the effects team replaced McGregor's robe with a digital version, and then after the hug, switched back to real cloth. The digital cloth looks real because it hangs properly, and because the friction algorithm caused Dexter's hands to crumple the cloth rather than slide across it.

"Mainly what we've done, though, is make it easier for the artists to do their job," Rapkin says. "We've given them more control over different aspects of the simulation so they can change parameters in small areas. We also added feedback so they can see what's going on."

The 352 cloth shots ranged from something as simple as the reins on a so-called "air whale," to Taun We and Lama Su's diaphanous skirts, to Jar Jar's Senatorial costume. Most of the characters required two layers of simulation, but Jar Jar's costume, which had four, was the most difficult. Thirty-one creatures in all needed cloth simulation; many shots had more than one cloth simulation. James Tooley, technical animation supervisor, led the simulation team and also managed character set-ups.

Making Wrinkles
"There are three aspects that make clothing work," says Tooley. "Tailoring, resolution, and collision." His team of 8 to 12 people discovered new methods for making cloth look realistic in each of those aspects.

First, Tooley worked with the modeling department to tailor useful garments. Rather than stitching panels together, the team discovered it was better to sculpt the garments on the characters. "We created shapes that looked like they were inflated with air," he says. The simulation team turned those B-spline models into a fairly continuous piece of cloth with a fairly evenly spaced topology that was then converted into a fairly high-resolution polygonal mesh for the simulator.

"I noticed that many people use lower resolutions because it simulates faster," Tooley says, "but I remembered John Anderson [former chief scientist at ILM] saying the higher the resolution the better." In cloth simulation, wrinkles are the goal, and it turns out that the higher the resolution, the finer the wrinkles.

The wrinkles are caused by collisions that happen when the character moves. "Most of our collision objects for the characters were volumes," says Tooley. Put simply, the team created rigid volumes (made of non-deforming geometries) that represented the characters' body parts. The volumes were needed so that when cloth sank into a character's arms, legs, or body during a simulation, the simulator could calculate, using data inside the volumes, exactly where the cloth was and get it out before the frame was drawn.

To control the simulation, long lists of parameters defined how the garment would move on its own, how it would be affected when it collides, and how it would interact with the environment. In addition, to better control cloth behavior, the simulation team used what they called "tacks:" Using painted maps, the team could assign specific parameters to small areas of a garment. For example, a tack might stiffen a seam. The team also used tacks to help control cloth when a character moved fast. "Yoda does these 720-degree spins in four or eight frames, and we have to make sure his robe and shirt and pants hang onto him," Tooley says. A carefully placed "protect" tack allowed the garment to inherit some of the character's speed.

At top: Digital Jango Fett fights with Obi-Wan. At middle left: Digital Obi-Wan. Above: The poly mesh used for cloth simulation. At right: Cloth simulations that produced realistic wrinkles made using a digital double for Obi-Wan feasible.

Coleman believes the realistic movement of the little Jedi's robe helps make Yoda's fight scene convincing. "The animation is good, but the clothing takes it to the next level," he says.

It's an example of the craftsmanship that is demonstrated throughout Episode II. "I would say the difference between what we did on Episode I and Episode II is that we had a more experienced crew," Coleman says. "Half my time on Episode I was spent worrying about whether we would get the movie done. I had climbed the top of that mountain so I knew I could get back up there again. This time, I could redirect that energy where it needed to be, on the screen and on the characters."

Next month, we'll look at hard-surface models, environments, and the big battle scenes.

---

Barbara Robertson is Senior Editor, West Coast for Computer Graphics World.

By the numbers.
Effects shots created:	2817
Effects shots used:	2000
Shots in the film:	2161
Minutes of CG animation:	70
Cloth-simulation shots:	352
Creature models:	About 66
CG Characters that talk:	12
Shots with CG Yoda:	127
Shots with JarJar:	32
Render Farm Processors:	1300
Desktop Processors:	1100
Processors running Linux:	50%