October 15, 2010
Riding the CG Wave
One of the most challenging assignments in visual effects is simulating photoreal CG water on a large scale. It was only two years ago that the Academy of Motion Picture Arts and Sciences bestowed Scientific and Technical Achievement Awards to the software brainiacs behind water simulation, and the best-known uses of this technology have been in fantastical films such as 2012, Poseidon, and Pirates of the Caribbean (read more about the water simulation technology). So it was notable to see water simulation playing a pivotal part in Warner Bros.' Hereafter by Clint Eastwood, a director hardly known for cutting-edge fantasy effects. Yet when Eastwood read Peter Morgan's script for Hereafter, he knew he would need to simulate a terrifying tsunami in order to propel this tale.
When Eastwood sent the script to Michael Owens, a former ILMer who's been his visual effects supervisor for the past decade, his message was, "Let me know what you think." Owens had overseen the digital crowds for Eastwood's Invictus and flotillas of warships for Flags of Our Fathers, but this challenge involved a level of complexity that they'd not tackled before. Hereafter, their ninth collaboration, would require what Owens calls "platformed" effects-effects that are meant to be noticed. "This was a more platformed thing because everyone knows we didn't have a tsunami on set."
Creating a terrifying flood that sweeps away a main character was crucial, especially since it comprises the first 9 minutes of the film. Actress Cécile De France, who stars in Hereafter alongside Matt Damon, is walking through a beachside village when the tsunami hits. Her experience of drowning, glimpsing a "herafter," and then being revived profoundly affects what happens next.
Owens replied to Eastwood's query by saying, "'We'll use a location for the street scene, but quite frankly I think everything else will be virtual.' Clint understood and agreed," he says. Owens said that they would need to storyboard and possibly previsualize the tsunami so that they'd know to approach it. "Clint never storyboards sequences himself, but he's always been very respectful when I've requested it because I only do it when it's really, really necessary. For this film, it really helped him to solidify in his mind the visual of the script. Then he lets go of it and goes off and shoots."
The prolific Eastwood was already in England shooting Hereafter while Owens was completing the post effects on Invictus, so the overlap was intense. In designing the tsunami sequence, Owens scoured footage of the 2004 Asian tsunami, and used some shots of it as placeholder images as the sequence design took shape. He hired visual effects art director Peter Rubin to draw the boards, and began interviewing facilities to handle the CG water simulation.
But most pressing of all was preparing to photograph De France in the water tank at Pinewood Studios while Eastwood was still shooting in England. Owens recalls Eastwood saying, "'Don't worry; if we make a mistake we can always come back. But let's see if we can do it.' So I put together a whole shoot with the tank," he says. Since Owens was still in North America finishing Invictus, to prep the shoot in London he hired Scott Squires, an Oscar-nominated visual effects supervisor and a fellow alum from ILM. Because the lighting was tricky, they used cineSync to conference with Hereafter DP Tom Stern and go over the storyboards. "Then I flew over a couple of days before the tank shoot and we shot it on the production's last day in London," Owens says. "We got a great deal of footage of Cécile in that water environment and wound up using most of it."
The only other real footage in the entire tsunami sequence was shot near the ocean in Maui, which was dressed to look as much like an exotic village as possible. "The only footage we planned to shoot for plates was Cécile walking up the street," Owens explains. "As soon as she gets hit by the wave, that's the end of the plate. But once we got to Maui, Clint had this other notion. He had seen all the footage and thought it was very good, but there was something not quite organic enough. When you have a bunch of guys with paddles disrupting the water during a tank shoot, it isn't a natural environment for an actress to be in. So when we were in Maui, Clint said, 'What if we took her into the surf and see what we get?'
"So we photographed her in this surface water. That day, there were lots of undulating swells, and you could see her absorbing the environment." That footage, combined with the tank footage from Pinewood, became the only physically captured water shots in Hereafter. The rest of the tsunami sequence-comprising about 100 shots in total-was purely digital.
For this, Owens hired Scanline LA, a three-year old production offshoot of the German company that had won a Sci-Tech Award for its Flowline simulation software. The company had created floodwaters for 2012 and the liquid battlefield for 300. Supervising Scanline's work on Hereafter would be Sci-Tech Award recipient Stephan Trojansky, along with Bryan Grill. Owens worked with them to develop the storyboards into a full-fledged previz.
Throughout the process, Owens knew that he shouldn't get to attached to his design for such a complex sequence. "Clint values previz a great deal, and he wanted the crew to look at it so everyone understood what we're doing," he says. "His method is to study it and then completely shoot from the hip. So even though Clint thought the previz was great, we didn't actually shoot it. After we shot everything, I re-edited it to make all the ends meet. Very few filmmakers allow themselves to do that. It's a little less polished-on purpose-and I think that adds more believability to the visual effects in a non-effects-driven movie."
Owens stresses that the key thing to remember about Hereafter is that it not a film that takes place in a supernatural realm. "It's really a romantic movie about people trying to deal with the Hereafter who fall in love. So the tsunami sequence needed to be captivating, but not upstage the story. The interesting thing about working with Clint is that he gives you creative, financial, and technical maneuverability. If you have nowhere to move creatively or financially and have to solve something technically, it really limits your options. But Clint has always allowed me room to maneuver, and if the edit changes, so be it. Nothing is that precious to him."
Which is probably a good mindset to have for anyone attempting to work within the highly iterative process of simulating a gigantic flood. Owens had chosen Scanline because the layers of details they could capture made the water look absolutely photoreal. To do that, Scanline's Trojansky says, "You need to go all the way into the deep hell of the physics of water. You need to have a simulator that can simulate a droplet of water that's photoreal, and then apply the same dynamics on a large scale and still maintain the fine details."
After six years of working on water, fire and smoke simulation, Scanline has developed methods that allow artists to control sims using key frames. This enables clients like Owens to tweak the simulation results for the intended effects.
"It's an iterative process," Trojansky says. "You set the parameters for the simulation and let it go. It's very unlikely that everything will do what you want at the same time. The randomness and the physics play with you. Instead of being completing dependent on the randomness of the physics, you go from rough simulation to finer simulation. The first simulation gives you overall motion and how far something travels. That runs in realtime, interactively, and for the director, that's often the most important because he can use it to design his shot."
actors who were photographed in the tank and the open ocean. "We had to find a way to track the real-world water characteristics exactly to the simulated water. So that the closer you get the character, the more that the CG water does exactly what the live action water is doing," Trojansky says. "We tracked the camera, the movement of the character, and the water motion itself, which was pretty tricky. We had to get a polygonal representation of the water surface and roughly get the movement of the waves. Then we could take the tracked motion of the water and apply it as a constraint to the simulation in a soft way. So where the live action plate ends, the CG simulation behaves exactly like the tracked motion. You basically create a feathered range from the live action to the CG."
"The job involved not only matching the water," Grill adds. "We had to have the wave take the character and move her down the street. When they shot the plate, the camera was locked. But in the final shot, we're moving down the street at 30 miles per hour, so we had to put in camera moves. It was amazing to take something that was so straightforward and add danger to it."
The tsunami also sweeps cars and debris alongside De France and causes CG-modeled buildings to collapse into the water around her. "The dynamics of the debris had to affect the water," Trojansky says. "Once we roughly defined where the debris and the water went, then we up-rezzed this and we ran it in refinement with photoreal details."
"When you get to that point," Grill adds, "the creative part is trying to keep what works and fix what isn't working. Every time you run a simulation, you don't get the same response, so you have to be creative in figuring out how to keep the best of both worlds."
While the main focus of the tsunami sequence is on the fate of De France's character, she's not alone in this disaster. But the other victims populating the sequence were primarily digital doubles. "We shot extras running, and once we got to the point where they were hit by the wave, we removed them and replaced them with digital doubles that would interact with the wave," Owens says. Owens also had a scan done of De France, so sometimes even she was replaced by her CG double.
Owens directed the motion-capture sessions at Giant Studios, using a rig that allowed the mo-capped actors to rotate freely on any axis. Over the course of five days, Owens notes, "We did the mocap several different ways, where we yanked people and pushed them and had them jump." Scanline Animation Supervisor Chad Finnerty then used this data to make the digital doubles react to the water simulation of the wave.
"We had to bring in stunt men to simulate being on the surface of the water," Grill says. "The hardest thing in dealing with the motion capture was dealing with how a person reacts while they're swimming if they're not actually in water. It was trial and error until we got to the point where we were able to look at the motion capture within our water sims and get a sense of the speed and the movement. Then when we got that into our 3D software, we were able to animate on top of it. You want the character to have a certain motion and speed throughout the scene. The water simulation is moving at a certain speed, so there was a lot of creative tug and pull. The characters can't move faster than the debris in the water. Sometimes we'd have to change the shot if it didn't look plausible."
To achieve all of this, Scanline used a variety of tools, in addition to its Flowline simulation software. "Flowline is integrated into [Autodesk] 3ds Max and the rendering engine V-Ray [from Chaos Software]," Trojansky explains. "We also used Massive and [Autodesk] MotionBuilder for the character animation, and then everything was composited in [The Foundry] Nuke X."
Owens had warned Eastwood that the tsunami sequence had by far the most complicated effects of their decade-long collaboration. "He just said, 'You'll figure it out,'" Owens says with a laugh. "He trusts me more than I sometimes wish he would!"
Eastwood already has Owens prepping Hoover, the story about the legendary FBI chief starring Leonardo DiCaprio. "Clint's never done digital makeup like that before," Owens says. "It will have to be at least partial prosthetics. But he's just rolling with it. He's not fazed at all about the technology."
If Owens himself harbors any reservations, he's not admitting it. "Every once in a while, I let Clint know if I'm especially worried about a particular thing," he says. "And because he's so secure and not egotistical, he'll say, 'Don't worry, Michael. We'll cut around it, or we'll shoot something else.' But I hardly ever have to ask him to do that because I know we'll make it work. Of course, if you keep pulling a rabbit out of the hat, people get used to thinking, 'What's the big deal?' Sometimes I feel like saying, 'Well I just about killed the rabbit! You can't do that all the time!'"