he devil’s motorcycle-riding bounty hunter got off to a blazing start despite the critics’ damp towels by whipping up more than US$44 million at the box office. ‘Ghost Rider,’ based on a Marvel Comics character, centers on motorcycle stunt rider Johnny Blaze (Nicholas Cage), who, after selling his soul to Mephisto (Peter Fonda), turns into a fiery Ghost Rider at night.
To create the 600 visual effects shots for the film, vfx supervisor Kevin Mack relied on his home base, Sony Picture Imageworks, with an assist from CafeFX and Digital Dream. “We did everything we could at Imageworks, but CafeFX did a lot of the one-offs,” says Mack.
“For a shot in which we meet Blackheart (Wes Bentley), the villain, they added a stormy sky and fiery rain, and they also did shots of both Blackheart and Mephisto where we did subtle quick things like little flashes of flesh peeling back. But the big things they did were introducing the water and dirt demons. Those shots were all CG. And, Digital Dream did a lot of nasty rig removals.”
Imageworks created the skeletal Ghost Rider demon, built and animated his hell cycle, and set both on fire. In addition, the studio created other elemental demons - earth, wind, and water, 10,000 wraiths, and several environments.
Scorchin’ Models
Modelers at Imageworks worked from cyberscans to build digital doubles in Maya of Nicholas Cage and his two stunt doubles. (One stunt double rode Johnny Blaze’s Harley, the other rode the huge “hell cycle.”) In addition, they built motorcycles and a skeletal, demonic horse.
“The hell cycle was probably one of the most complicated models we’ve done as far as the amount of geometry and detail,” says Brian Steiner, CG supervisor. “Usually, we create a whole model and then spend a week adding detail. But we built this piece by piece at high resolution. Every couple of days, the modeler would bring out another little section.”
For the horse, the modelers started with a skeleton, built a rough body on top, and then added a muscle system and interconnecting tissues. “Basically, we ended up with sheets that connected piece to piece,” says Steiner. “We had to do a lot of chaining to make them look like tendons that connected one part to another. Each piece was simple, but when added together, it was complex.”
Rigging the rides was equally complex. “For the motorcycles, we started with the Harley, which was a simpler design,” says Steiner. “We tried to make it as straightforward as possible for the animators.” Controls built into the rig, for example, automatically tightened brake lines and banked the bike when animators turned it around corners.
Once the Harley rig worked the way they wanted, they migrated the rig to the hell cycle. “It didn’t have brake lines, and the proportions were different, so we modified the basic controls,” says Steiner.
The horse was actually more difficult. “It had a very long backbone which was complicated to move right when it gaited, but the muscle pieces were the biggest problem,” says Steiner. “We built a volumetric deformer that was like a little muscle system, so when the muscle got shorter it would bulge out.”
A separate system put skin on top, but only in some areas; much of the surface was transparent. “Trying to get the muscles, the interconnected tissue and the skin to work together was painful compared to most characters.”
Because the elemental villains - wind, earth, water - appeared in both their human and demonic forms, the effects crew scanned the actors, and then created digital doubles and rendered them as if they were human. Particle effects combined with compositing tricks created the illusion that the wind character was made of dirty air.
“It took a fine balance,” Steiner says. “If the air is clear you can’t read the character, if it’s too thin it looks like a ball. We have the face break into pieces so you’d see multiple versions. And, we did the same sort of thing with the dirt guy.”
The main demon, though, Ghost Rider, was a special problem. “He’s a leather-jacketed biker guy with a flaming skull and hands, and his bike wheels and motor are on fire,” Mack says. In addition to matching the skeletal character to reference of Nicholas Cage and his stunt doubles, the crew needed to give the skull an emotional performance. At first, they tried switching skulls with different expressions between shots, but ultimately, they found that using the fire to portray emotion was more effective.
Light My Hellfire
“The hellfire has always been described as a supernatural flame,” says Ken Hahn, digital effects supervisor. “It’s not a consuming flame. It doesn’t create smoke. It just exists. We used it to tell the emotional content of Ghost Rider. When he sees Roxanne, the reds go out and it’s a more subtle, subdued type of flame. But when he gets really angry, the flames become hostile and dangerous.”
With a few exceptions, Ghost Rider’s fast-moving fire is always CG, a computational fluid simulation brought under control by Imageworks’ Patrick Witting. “We used the Maya solver, but only for the core calculation,” Mack says. “We built a Houdini front end and back end as well as a renderer.”
To modify the fluid variables in the Maya solver, that is, the velocity, temperature, density, and amount of fuel, and to specifically place the fuel, Witting wrote Maya plug-ins that read data from Houdini texture maps and expressions. “We could use painted maps to be specific about where the fuel is,” Witting says, “or, because Houdini is very procedural, we could write 3D and 2D noise functions to create lumpy shapes or areas without fuel.
The Maya plug-in read the Houdini information and modified the fluid variables. That gave us a more direct way of interacting with the solver than with forces. There’s a limit to what anyone can achieve if they’re trying to do effects animation only by manipulating forces.”
