COVER STORY: PLAYING WITH FIRE

Mack, from Sony Pictures Imageworks (www.sonypictures.com/imageworks), met very early on with director Johnson and his team, who had only done some stylized artwork prior to the meeting. “They wanted to know my take and how I would approach it,” describes Mack. “I told them that I would go with a computational fluid dynamic simulation for all of the fire and a CG skull replacing the actor’s head whenever possible, and that it has to be all CG.”

He also proposed an interactive light system, which he describes as kind of a ski mask with flush-mounted, flat LEDs to be computer controlled to fluctuate their light pattern, creating an interactive light on the actors’ shoulders. “So if they were standing in front of a wall it would light it up,” he explains. They also put these LEDs on the motorcycle wheels to light up the bike and the road itself. “We could put in all this CG fire, but it would look weird if it wasn’t interacting and casting light on the practical elements.”

Imageworks had neither of these technologies before Mack suggested them, so after the meeting, the team got busy developing the proprietary computational fluid dynamic sim tools necessary to create these effects — they built them off Autodesk Maya and Side Effects Houdini, running mostly on Linux workstations — and started searching for an LED that was thin enough and bright enough for the interactive lighting system. Turns out an LED flat enough for their needs didn’t exist at the beginning of the production, but came out shortly after.

“This was a tough one because we didn't have anything that makes the usual CG character shine,” describes director Johnson. “We didn't have any eyes or lips or wrinkles — all those things that make a great CGI character we didn't have. So my goal for Kevin was to really help the fire become an extension of Ghost Rider’s personality, to show different moods and character traits, to get everything across we couldn't do with the usual facial features we were missing.”

To get a better hold on the look of the fire, Mack did a test where he actually set fire to a prop skull and a mannequin and shot it. “It confirmed what I suspected, which is that real fire doesn’t look that great unless you expose for it, but when you do, everything else in the scene goes black. Also, at 24fps fire tends to get real hard edged and strobe-y. The two cheats I proposed were to slow it down in our simulations and always optimally expose our CG fire so regardless of our environment and how it would actually photograph, it would be rich in color and detail… and that gave it a more distinctive, beautiful quality than real fire.”

Mack admits that the fire was a tough build. “It took quite a while to get that working. Patrick Witting, here, wrote the system, which is a real pipeline and very robust. It has all kinds of controls; so it gave us the ability to art direct the fire.”

The skull, which was modeled in Maya, is CG throughout the film. “We actually scanned a human skull [obtained from a museum] and then scanned Nick Cage and did dental castings. We then modeled this human skull that we scanned to fit into Nick’s head,” describes Mack. “Basically, we modeled it to match him, kind of like a forensic scientist would do. And using his teeth we adjusted it so it really felt like it was Nick’s skull.”

It wasn’t all fire and skulls for Imageworks. They also created The Hidden — three elemental demons who each have a signature effect: the Water Demon forms out of water and can turn into water; the Earth Demon forms out of earth and turns into dirt; and the Wind Demon becomes the wind and turns into vapor.

“I knew that fighting people wouldn't be much of a challenge for Ghost Rider,” explains Johnson, “so I wanted him to go after these rebel angels who were thrown out of  heaven and have been hiding in the elements all these years — so they’ve actually become the elements.”

For the showdown at the end of the film, Imageworks used their own particle systems to create an effect for The Wraithes, which are decrepit, flying mummy corpses who exude an inky black vapor. They are all CG, modeled and designed in Maya and Pixologic ZBrush. They fly around and are summoned to enter and merge with Blackheart, the main villain, who at the end of the film transforms into a demonic figure.

“We used [this ‘Soul Mist’ vaporous] effect in a few different ways,” explains Mack. “The Wraithes are exuding this stuff and leave these inky black vaporous trails that kind of ooze out of their skin and into the air, and there’s thousands of them. But once they enter Blackheart his features change. We wanted to keep [the features of actor] Wes Bentley and not lose his face. So we tracked in a demon face that we designed and built in 3D, with Maya and ZBrush, and we used elaborate moving soft mattes — smoke and vapors — to reveal alternately the demon and Wes in varying percentages. So it’s constantly moving, depending on the mood of the moment. If he’s very angry he becomes the demon, and if he’s injured or set back, he would revert back to Wes.”

But Imageworks had another take on this Soul Mist effect for Blackheart, so instead of exuding out of him like with The Wraithes, it’s actually being materialized in the air and pulled into him. “So he’s actually materializing the vapor and it becomes visible as it gets close him and then it’s pulled into him. It was a tricky particle system to get them to be attracted to [Blackheart] and we had to track a 3D version of him in Houdini to serve as the attraction surface.”

One of the Ghost Rider’s main powers is that he can look into the eyes of an evildoer and judge them. They get sucked into his eye and go to a place where all of their evil actions are played out upon them, experiencing the suffering of their victims as punishment. “That was a really impressionistic, abstract sequence and we did two: for a mugger and for Black Heart at the end of the movie,” says Mack. “There’s a lot of fire elements in this effect — a spiraling vortex of fire in his eye created with a fire sim, but we also used some actual fire footage shot slow motion.” The compositing was done in Autodesk Inferno by Imageworks’ Christian Boudman.

Imageworks also created CG stadiums, helicopters, football fields, motorcycles and riders. “At one point Nick Cage jumps over a football field with a bunch of helicopters with their blades spinning, so that’s mostly CG,” he says.

One of Mack’s favorite effects was when the Ghost  Rider is at the top of an arch on a bridge with cops surrounding him. “He slides down the support beam of this arch and drops into the river and sinks. The cops are looking over the edge and fire and steam glow out of the water, and he just bobs out like he’s on a jet ski. He’s still on fire and the water interacts with him and the fire. Then he flips off the cops and hydroplanes down the river. We did fluid sims, and the bike and rider are all CG. It’s pretty awesome,” he says.

Imageworks has an elaborate infrastructure and pipelines in place for handling data. Their PST department watches the renders, checks them and constantly manages the disk space and allocates the CPUs.

They use Pixar RenderMan for most of the standard work, but they wrote a renderer for the fire and used it also for smoke and steam effects.

In regard to the final renders of the fire, “Patrick’s system allowed us to crank out lots of low-rez iterations so we could hone each simulation,” explains Mack. “But the final renders used massive amounts of memory. For close-ups of Ghost Rider’s fire, we had to divide up each frame into slices to be rendered on multiple CPUs, because even a single frame required more memory than was on any one machine.”

While Imageworks created almost 300 effects  shots for the film, they had to outsource some work to CafeFX, Digital Dream and Grey Matter Effects. There were about 600 effect shots in all.