CG Superheroes: Body Building
Issue: Volume: 26 Issue: 7 (July 2003)

CG Superheroes: Body Building

By Barbara Robertson

It takes a great actor working with an inspired director to create a character that successfully portrays inner conflict. But when the script calls for that character to be 15 feet tall, full of rage, and for the most part unspeaking, the role offers particularly interesting opportunities. The Hulk, based on the Marvel comic of the same name, tells the story of Bruce Banner, a genetic scientist studying the effects of gamma radiation on tissue, who has a freak accident in the lab. Already troubled by nightmares and anxieties that trace to his childhood, Banner's inner rage now has an external manifestation: the angrier he gets, the bigger and greener he becomes.

Filmmaker Ang Lee could have created a Hulk that was a simple giant wreaking havoc on the world, and certainly Lee's Hulk causes his share of destruction. But rather than focusing solely on what the Hulk could do, Lee chose to also show what the Hulk was feeling—to create a "Greek tragedy" with comic book styling. As a result, Universal Pictures' The Hulk, scheduled for release June 20, gives audiences an approach to filmmaking that's unique, from the split-screen memory montages to the superhero himself, arguably one of the most successful digital humans to star in a feature film.

Because the Hulk's face fills the screen, the texture map for his left cheek alone was painted at 1024 x 2048 resolution. ©2003 Universal Studios. Courtesy Industrial Light & Magic.

"Ang said at the beginning that he wanted this to look like a movie, not like it was real," says Dennis Muren, senior visual effects supervisor at Industrial Light & Magic, where the visual effects were created. "He wanted it to look handmade, by people; to be a piece of art. He loves art and the feeling you get when you see it."

To help realize Lee's vision, Jules Mann and Wilson Tang, visual effects art directors, began working from a rough maquette created by production designer Rick Heinrich and approved by Lee—to create concept art the visual effects crew would reference. "They had cast Eric Bana as the lead," says Mann. "We had to come up with reference art that showed how he transforms into the Hulk, how the Hulk moves, his hair and makeup, his clothes, his muscles, and how he interacts with the environment."

Mann's cubicle walls are papered with color prints and sketches of Hulk's facial expressions, of Hulk in the desert with sand on his back, of Hulk's internal conflict, and more, many of which were painted in Adobe Systems' Photoshop. On his desk is a stack of paper three inches deep. "This is last month's art," he says, and does a quick calculation. He estimates that the two art directors and their team of eight artists have created more than 5000 pieces of concept art.

How did this concept art become a huge, fully realized CG character? One pixel at a time.

On the monitor in compositing supervisor Marshall Krasser's office, Hulk's face glares out at passersby; a face so big it doesn't fit on the screen. "It's going to be this big on the movie screen, and it's the worst-case scenario," Krasser says, describing a scene in which the camera cuts from a close-up of a real actor to the digital actor.

To create Hulk's skin, ILM's visual effects crew combined painted maps with procedural shaders to produce the color, pores, wrinkles, and other details, such as this wound.

Preparing Hulk for close ups took months. Beginning two years ago, Gerald Gutschmidt, CG supervisor, led R&D efforts for Hulk's skin. About 18 months ago, Susan Ross, Viewpaint (ILM) supervisor, began painting texture maps; Hilmar Koch, sequence supervisor for Hulk's skin, began working on shaders; and Aaron Ferguson, creature developer, began sculpting shapes for Hulk's muscles.

Working in Avid's Matador, Ross painted 130 different types of texture maps—dirt maps, sand maps, color maps, bump maps, specularity maps, and so forth—to create the look of Hulk's skin in all his environments. For any one of those maps, she might have made an additional 300 to add detail and texture and to control procedural textures. "We're talking thousands and thousands of maps," she says. Map resolution depended on the part of body being painted. The small area over Hulk's left cheekbone, for example, was painted at 1024 x 2048 resolution.

By using a pose-based system in which shapes were invoked by joint position and rotation, the creature-development team at ILM created Hulk's muscles.

Yet, remarkably, Ross painted all the maps with a one-pixel brush, the finest brush she could use. "I get a lot of detail," she says. "I scribble color over color over color, and it creates something that's very human."

Because Hulk's size changed with his mood, the effects team created 9-foot, 12-foot, and 15-foot Hulk models in ILM's own Isculpt software, plus a digital double for actor Bana. Although they would eventually tweak maps from the 15-foot version for the other models, Ross had already painted maps for each. "I painted green for so long that when I turned away from the screen, my room would look pink," she says.

Some of the texture maps Ross crafted controlled subsurface scattering, which gave Hulk's skin translucency. "We used it on the whole body, but isolated some areas where we wanted more of it," says Koch. And painted gray-scale texture maps described pore density on Hulk's skin.

To procedurally generate the pores and a web-like network of small wrinkles between pores on the surface of the skin, Koch, who admits to spending an inordinate amount of time staring at his hand during the past 18 months, created sophisticated shaders in Pixar's RenderMan that, simply put, would arrange pores that he'd pour on Hulk's skin. "I used an approximation of a Poissant distribution, which in essence says the points all want to be the same distance from their neighbors," he explains. "Then I wrote shaders that would look at the points, render them into the shapes of pores, and create wrinkles between adjacent pores." An additional shader gave the resulting cellular structure directionality. Lastly, Koch wrote a program to blend all the texture maps painted by Ross with the procedurally generated pore and wrinkle patterns.

When Banner transforms into the Hulk, his body grows, his skin expands to accommodate the muscles bulging underneath, and he turns green. Rather than animate the expanding muscles by hand and then using simulation to stretch the skin, the team decided to sculpt shapes to gain greater control. To do this, they built geometry for individual poses based on joint rotations. "For some joints, like his fingers, we could get away with a shape or two," says Ferguson, "but we had to sculpt 42 poses for each shoulder." Using height and spin values derived from joint position and rotation, an in-house program calculated the percentage of various shapes needed to make Hulk's form match his movement. Similarly, the shapes from one model size would blend into another during Banner's transformation into the Hulk and from one sized Hulk to another. The resulting shapes, in turn, determined how the skin looked.

"The values from the shape curves gave the technical director an indicator, on a point-by-point basis, of what percentage of a shape is Banner and what percentage is Hulk," says Gutschmidt. These values were sent to a shader that would, in effect, mix the skin maps using the appropriate percentage of Banner skin and Hulk skin. A so-called "riverbed" texture on top completed the illusion that the transformation happened at a cellular level. "We wanted Hulk to flow into Banner, not fade in," he says.

All these efforts helped make Hulk's skin look realistic. To make it move realistically, creature developers created 62 springs, jiggle muscles if you will, that reacted to dynamics. When the Hulk ran, for example, these jiggle muscles helped the skin flex on his legs. Lastly, the creature developers used a technique called "skin relaxation" to make the skin look like it was stretching and sliding properly. "If you don't separate the texture and the form, it's real easy to get a rubber-suit look," says Ferguson.

Compositors helped blend Hulk into the environment with practical dust and procedural shaders (top), working from concept art (middle), created by Wilson Tang.

Meanwhile, to give Hulk hair and help keep his short hair from looking like a wig hat, sequence supervisor Pat Conran led a team that rewrote ILM's fur generator so that tufts and wisps of hair could be animated against the general hair movement. They also added peach fuzz, stubble, and other body hair to Hulk's skin.

Finally, to put the "photo" in "photoreal," Krasser wrote a plug-in for ILM's CompTime compositing program that softened hard CG lines around Hulk's eyes, nose, and other areas without affecting the general sharpness of his skin by displacing pixels in these edges. "That diffusion made it seem more photographic," he says.

Separately, a team of approximately 45 animators led by Colin Brady began creating the Hulk's performance based on animatics created with Softimage|XSI, and with constant direction from Lee who moved his office to ILM for the postproduction. "Ang directed the actors extremely close-up and personal, and he did the same thing with us," says Muren. "The animators were directed down almost to the pixel. He had in his mind from the beginning what he wanted this character to look like and how he wanted it to move."

In fact, Lee himself provided much of the animation reference, at times even donning a motion-capture suit. "More than any other show, the secret was the reference," says Brady. "I'd say a quarter to a third of the show relied on motion capture from Ang Lee, but even more important than the motion-capture data was having one model to reference Hulk to. My biggest fear was that we would create a generic guy." The animators used motion data particularly from Lee's upper body to create Hulk's performance, and also used bits of that data, all captured with Vicon8 system, to cut and paste "noise" into keyframed animation.

For the other two-thirds of the performance, Brady's team used video reference of Lee, of Olympic athletes, and of the animators themselves. "I think my MiniDV was one of the most important tools I had," Brady says, pointing to a small Sony video camera. In addition, the crew referred to and sometimes used rigid body simulations of Hulk thanks to a new in-house system that incorporated keyframed animated cycles within a simulation. Hulk, after all, was bigger than any athlete.

"We'd create tests to see how he'd fall down," says Scott Benza, lead animator. "Would his upper torso fall first? Would his hips twist around? Also, we couldn't shoot reference for things that would hurt people." Even so, many of the Hulk's movements were purposefully physically impossible: He has super powers. "Ang wanted him to move faster than reality," says Brady. "He'd say, 'We're not making a dinosaur movie.'"

To animate the Hulk emerging from the immersion tank, animators started with motion data captured from director Ang Lee's performance of the superhero throwing a tantrum.

To create and fine-tune Hulk's performance, about half the animators worked in Softimage 3D and half in Alias|Wavefront's Maya. For his facial performance, they used ILM's Caricature software and a library of approved expressions. "Within these, you could have all kinds of twitches and variations, but they were a good starting place," says Brady. "We'd start with our expressions and then Ang would say, 'Make it angrier, angrier,' so we would push it further."

In one shot, Hulk breaks out of an immersion tank with a roar. It's a shot Brady particularly likes. "Someone said it looks like a baby throwing a tantrum," he says. "That's exactly what Ang was looking for. If someone had told me we would have been able to get pain, anger, and pleasure all in the same action, I wouldn't have believed him."

Adds Mann, "When the film came here, we thought we were going to be rehashing existing themes. Boy were we wrong."

Barbara Robertson, contributing editor of Computer Graphics World and a freelance journalist, can be reached at

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