X-Men, a Marvel Comics classic, undergoes a CG transformation
By Debra Kaufman
The mutant superheroes and villains of Stan Lee's X-Men have graced comic book pages for decades, and the classic Marvel series has been bandied about in Hollywood as a potential screen project for years. But bringing X-Men to the big screen in a way that would make the most of its characters' extraordinary powers and spectacular transformations was, until recently, a virtual impossibility.
"A big-screen X-Men could have been done earlier, but not with the same type of look that we gave it," says visual effects supervisor Michael Fink (Braveheart, Batman Returns), who helped make this summer's X-Men feature film a reality. By using innovations in digital effects to achieve the extraordinary transformations of live actors into peculiar mutants, Twentieth Century Fox, in association with Marvel Entertainment Group, overcame what was once a major stumbling block to the property's movie debut.
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| Innovative digital effects played a key role in the X-Men's transition from comic book characters into believable live-action mutants. Animation facility Kleiser-Walczak performed some of the more compelling transformations in the film-those of metamorph |
The X-Men film features a darker, edgier look than the more "cartoony" X-Men comic books. But like the comic, the film addresses complex social issues such as racism and bigotry in an action-packed setting. In fact, from the beginning, the filmmakers signaled their intent to make this an atypical "comic book" film through their choice of director, Bryan Singer, who helmed The Usual Suspects and Apt Pupil.
Not known for his use of visual effects or action-adventure plots, Singer has instead earned a reputation for character and story development. As a result, Singer and creative partner (and executive producer) Tom DeSanto used those strengths while creating the X-Men story line that would capture the true characters and mythos from the '60s comic series. "I was determined to make the story as believable and real as possible," says Singer.
Though films focusing on character development usually do not require visual effects, in X-Men, all the main, live-action characters possess unusual powers and undergo sensational body transformations that could not have been done convincingly without computer-generated imagery. These include the good mutants who work under the guidance of Professor Xavier to protect a world that fears them, as well as the professor's former colleague and nemesis, Magneto, and his evil brotherhood of fellow mutants.
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| Digital Domain used unique lighting and modeling techniques to mutate Senator Kelly into water. The column at left shows the effects layers for the shot and at right, the progression. (Images courtesy Digital Domain. ) |
The movie contains more than 500 effects shots, which were largely divided between facilities by character. With the assistance of visual effects producer Denise Davis and visual effects wrangler Bill Maher, the effects team oversaw the creation of eight characters with different capabilities and genetic mutations, in addition to an entirely virtual set. The large (and constantly increasing) number of shots in an ever-shrinking time frame resulted in the most intense schedule that Fink says he's ever experienced.
In one of the film's more compelling visual effects scenes, villain Magneto (Ian McKellan) turns US Senator Robert Kelly (Bruce Davison), a foe of the mutants, into an altered being so he can experience the mutants' persecution firsthand. Kelly escapes Magneto's prison and flees to Professor Xavier's laboratory, where his mutancy goes wildly out of control and his skeleton and internal organs begin to show through transparent skin. The sequence culminates with the live actor decomposing into a puddle of water.
Before creating this tricky 3D transformation, the Digital Domain (Venice, CA) team, lead by CG supervisor David Prescott and technical director Sean Cunningham, had the following shots at their disposal: a motion-control move of Kelly, from which the animators used a still for Kelly's facial texture; a lighting reference; a clean shot of the lab bed on which the transformation occurs; and a passing shot of a large bag of water, which at a precise moment is sliced open so the water spills over the bed. This "water" pass gave the group the timing needed to transition Kelly from a real actor to a water puddle.
Modeler Dustin Zachary started with a cyberscan of Kelly for reference, over which he created a subdivision cage in Maya. (Creating a new model required less time than cleaning up the scanned data.) How ever, the scan data served a valuable purpose in that it enabled Zachary to accurately match the proportions of his model to that of the actor in the live shot. After using Maya's subdivision surfacing for preview, the group then pulled the model into Houdini 4.0 to take advantage of that tool's proceduralism capabilities.
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| The film's action is staged in present-day New York City, and the climactic scene makes generous use of its most famous landmarks, but not a single shot was actually filmed there. Instead, Matte World Digital created an entirely digital 3D back lot, which |
Also using Houdini, Cunningham modeled a bag shape that represented the bag of actual water. Then, over the course of the shot, he texture-mapped the model of Kelly onto the bag, so the Kelly model slowly assumed the shape of the bag. According to Cunningham, he controlled this transformation at the vertex level, where Kelly's vertices were black, meaning the model retained Kelly's shape prior to transformation. As the values increased to white, Kelly took on more of the bag's shape.
"I could change the point colors over time, doing gradual wipes along the length of his body," Cunningham says. "As I animated this wipe through his body, the Kelly model assumed the shape of the bag, and as I animated the bag, the Kelly model took on the animation of the bag."
Lighting this scene required yet another trick, incorporating an innovative use of newly published research by scientist Paul Debevec, known for image-based lighting techniques that enable CGI to be lit with the actual lighting from a live-action set. The Digital Domain team already had a "light pass" of the scene that made use of a light probe, a perfectly mirrored chrome sphere that captured the position, color, and brightness of all the lights in the scene. Debevec's research is based on creating lighting exposures from the most underexposed to the most overexposed. But Cunningham had only one pass at the one exposure, so he simulated the other exposures to derive and match the color temperature of the lights.
The final calculations for the transformation were done in Houdini's V-Mantra renderer, new with Version 4 of the software.
In the last step of this complex 10-second liquid transformation, Digital Domain (Venice, CA) compositor Claas Henke used a 2D morph of a close-up still of Kelly's face, performing 2D warping and painting tricks so Kelly's eyes rolled around and back into his head.
Rogue (Anna Paquin), a reluctant teenage mutant, has the ability to absorb the life force and memories of any person she touches, an ability illustrated for the movie by effects studio Hammerhead Productions (Los Angeles). When Rogue exerts her powers, we see subtle movement as power surges through her body and into the person she's in contact with, an under-the-surface effect in which blood vessels push against the skin.
The biggest challenge in creating this effect, says Ham mer head visual effects supervisor Theresa Ellis, was tracking the human movement, including different parts of the face, upper body, and hands for Rogue and the other characters. In fact, Hammerhead is well known among visual effects cognoscenti for its software that enables 2D or 3D tracking using points in an image. Written by Hammerhead partner Thad Beier, the Unix-based rastrack program won the studio a 1998 Scientific and Technical Achievement Award from the Academy of Motion Picture Arts and Sciences.
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| When Rogue touches other people, she can absorb their memories and life force. To create this effect, Hammerhead modified its rastrack software to drive its in-house morph program. (Image courtesy Hammerhead Productions.) |
In X-Men, Hammerhead modified rastrack so that the output of the tracking drove Hammerhead's in-house morph program to warp a painting to follow a moving sequence. So rather than create a painting for every frame in the transition-which would have resulted in flashing and flickering as the sequence played-the group could warp the same image from frame to frame as the tracking kept the painting "glued" to the image.
Hammerhead partner Rebecca Marie, who animated the Rogue effect, first used Photoshop to paint 2D images of the blood vessels that would appear under Rogue's skin. She then created highlights and shadows using various image-processing techniques, and the elements were composited with Hammerhead's proprietary software. "The trickiest part is putting all the elements together to create the illusion of reality," says Marie, "and it's not simply putting something on top of the picture."
With the power to transform into anything or anyone she sees, the evil and enchanting metamorph Mystique (Rebecca Romijn-Stamos) is a member of Magneto's evil brotherhood of mutants who masquerades as other people. During her transformations into other characters, she reveals her own physical persona, which is blue, nearly naked, and covered with moving scales. Performing Mystique's transformations from a series of live-action characters into a complex, photoreal 3D character was Kleiser-Walczak (Hollywood, CA). As Mystique's shape shifts from that of another character, such as a man in a business suit, she simultaneously turns blue, and thousands of scales emerge from her skin, similar to the ruffling of feathers.
To achieve this complex effect, Kleiser-Walczak's lead animator Scott Palleiko spearheaded the task using Paraform's still-beta version of its digital modeling software to convert the polygonal models from digital scans of the actors to highly optimized NURBS models. The group then added detail to make the NURBS models appear more lifelike, and refined the models for each transformation so that their skeletons corresponded and blended from one shape to another. Because every patch on the surface of the NURBS model corresponds to a patch on the "destination" model (Mystique's ultimate shape), this allowed for a smooth and seamless transition during the 3D morphs.
The team at Kleiser-Walczak experimented with many methods of choreographing the transformations, ultimately placing CG lights on the NURBS destination model, tweaking it, then animating the lights to create a series of moving white and black texture maps covering Mystique's entire body. The maps were fed into MEL scripts that controlled both Mystique's shape and appearance. One of the benefits of using Maya, says visual effects supervisor Frank Vitz, was that MEL enabled the group to write procedural scripts embedded in the same software package. "The net result was that, rather than the hard edge of a rotoscope, these lights created shadows and gray areas," he says. "The variegated edges move in an interesting fashion that would have been hard to do manually since it was based on the softer interplay of light."
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| Kleiser-Walczak used procedural and keyframe animation to ruffle Mystique's feather-like scales. (Image courtesy Kleiser-Walczak.) |
Mystique's scales, which cover 70% of her body, emerge through her skin during her transformations and grow to become anywhere from a quarter-inch to 4 inches long. Kleiser-Walczak animator Beau Janzen digitized the 10,000 scales on Mystique's body so the team could animate them individually as they broke through her skin.
To create the illusion of the scales growing, the artist employed a custom plug-in for Maya that used luminance values in texture maps to control the scales' final lengths-the luminance value in an area on the surface determined the ultimate length for a scale in that area. The texture maps used were those from the transition.
To produce a ruffling effect for the scales, the animators created keyframe animation cycles. Then, using the same Maya plug-in and texture maps as for the growth animation, they assigned particular animation cycles to the luminance values in the texture maps so the scales would ruffle as they grew. This combination of procedural and keyframe techniques provided automation with control-an animation cycle could be applied to large areas or individual scales, and the animators could tweak the animation of particular scales after the procedural animation had been applied. "The effect is very organic and dimensional," says Vitz. "A scale comes up over her back and will lie down out of sight. There's no doubt that this is happening on the surface of her entire 3D body, rather than painted on the front."
In addition to coordinating the unique and cutting-edge effects produced by the various leading animation houses, visual effects supervisor Michael Fink designed the CG effects for several other X-Men and their specific powers that appear throughout the film-from beginning to end. "We didn't save our big effects for the third act," he notes.
Indeed, bringing X-Men to the screen has been a long time in coming, but the film's seamless, spectacular effects have made it worth the wait.
Debra Kaufman is a freelance journalist, consultant, and teacher, who has covered the evolution of digital effects for more than 10 years.
A Sampling of X-ToolsSide Effects Software
Toronto
416-504-9876
www.sidefx.comAlias|Wavefront
Toronto
416-362-9181
www.aliaswavefront.comParaform
Palo Alto, CA
650-846-2100
www.paraform.comAdobe Systems
San Jose, CA
408-536-6000
www.adobe.comHammerhead Productions
Los Angeles
818-762-8643
www.hammerhead.com