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MillimeterBlue Crush
Sep 1, 2002 12:00 PM, by Ellen Wolff
Facing A Visual Effects Challenge
 Background plate of stunt surfer Rochelle Ballard. |
When director John Stockwell took on Universal Pictures' surf movie Blue Crush, he probably didn't expect to oversee any innovations in visual effects. This being his second feature (following Crazy/Beautiful), Stockwell's priority was getting performances from the young actors portraying daredevil surfers. Aided by the expertise of visual effects supervisor Jon Farhat and Hammerhead Productions' Thad Beier, the movie avoids the cliché of crosscutting between breathtaking long shots of stunt surfers and close-ups of actors in a tank.
Instead, famed surfing DP Don King shot dazzling footage of champion surfer Rochelle Ballard swooping right past the camera, water streaming across her clearly visible face. Then it was up to the visual effects team to convincingly replace her face with that of actress Kate Bosworth. The challenge “was that while the character was surfing she was also screaming, delivering lines and expressions,” explains Farhat. “We wanted to capture an actor doing that on film, and then stick that performance on the stuntperson's face so we'd have a photographic solution.”
 Kate Bosworth on set |
In the past, shots like this have been handled frequently by modeling a 3D-CG head using cyberscan data of the actor, and then animating it. “Simulating muscle and eye motion is extremely difficult, and it also removes the performer and the director from the process,” says Beier. “We thought that by filming the actress and using that footage, we could make it come alive in a way that animation never could.”
The process began during location shooting in Hawaii. Farhat had a face cast made of Ballard, and he fashioned a plastic mask that fit her face exactly. The mask had holes punched it in at crucial places, like her nose, forehead, and chin, so when Ballard put the mask on, the holes indicated where tracking dots should be placed. “Every time she was on camera,” recalls Farhat, “ the dots were in the perfect place.” Glowing yellow and black — to contrast with the bluish surf — those dots would later provide Hammerhead Productions with the markers to track the movements of the surfer's face.
Once the director had chosen the key surfing plates, the visual effects crew set up a stage to film Bosworth's face. Three locked-off cameras were synched and focused on a calibration cube. This setup provided a filmic area within which the actress could move her head — a virtual box that measured about a foot on each side. Two cameras were set at the actress' eye level, 30 degrees from the centerline, one on the right and one on the left. A third camera was on the floor on the centerline, looking up. The three cameras could capture footage of Bosworth's entire face.
 Three synched frames of Kate Bosworth's face |
Before each take, the actor and director would watch a video of what the surfer had actually done, and then craft a suitable facial performance. For each of the 15 shots that required face replacement, Farhat also changed the lighting in order to mimic the look of each plate shot on location. “Everyone wants to do flat lighting and then add 3D lighting,” Farhat says. “But that doesn't work. I promised Thad that I would get the best photographic match to the background plate that I possibly could.”
Once this footage was scanned, Beier's team set about tracking the actress' head to mimic the movements of the surfer's head. Hammerhead is known for its tracking software Ras_track, but this assignment required additional programming. Beier wrote new software called Obj_track 3 that figures out exactly how an object moves, given three different camera views of it. The software indicated which one of the three photographic angles of Bosworth's head to use. The result was a totally stabilized face texture of Bosworth that could then be applied to the footage of Ballard.
The tracking process was painstaking, however, since the background plates had been done with extremely wide-angle lenses that produced significant distortions. “Tracking those distortions was a real challenge,” admits Beier. “And there was often water on the lenses. Because we wanted it to look as real as we could, sometimes we'd have to remove the distortion to do the tracking and then put the distortion back in.”
 Finished composite with Kate Bosworth's face |
To complete the illusion, water was added over the replaced face as well. Hammerhead removed the water rippling across Ballard's face, put Bosworth's face in, and then added the water back on top of it. “Sometimes it was digital water, but several times we extracted the water on Rochelle's face and put it back on top of Katie,” says Beier. “There was enough contrast because the water was much brighter than everything else. We also pulled water from other parts of the scene and put it over her face.” Hammerhead used its Roto tool for the considerable rotoscoping involved, as well as its Z-animation tool. Rendering was done with RenderMan, and compositing was done with Hammerhead's Matte software.
The final step in the process required color correcting all the disparate lighting in the various background plates, which was also done digitally. E-Film digitally timed the entire film by scanning it on its Imagica scanner, a non-realtime system that provided a high degree of contrast control.
At the project's start, Beier wasn't sure if Hammerhead could accomplish more than six face replacement shots, but in the end all 15 were done. “I don't think anyone held back in terms of giving us the hardest shots they could find,” Beier says. “But what was really exciting was that the director got beautiful performances from Kate.”
“It's the first time we've ever put a director and his actor on a stage and let them work with what a stunt person has done,” says Farhat. “We can now take a photographic performance and put it into any world they want.”
Credit Roll
Director - John Stockwell
Visual Effects Supervisor - Jon Farhat
DP (surfing footage) - Don King
DP (visual effects) - Don McCuaig
Digital Timing - E-Film
For Hammerhead:
Visual Effects Supervisor - Thad Beier
CG Animator - Constance Bracewell
CG Water Animation - Jamie Dixon
3D Tracking - Joel Merritt
Rotoscoping - Gilbert Gonzales
Continue the discussion on “Crosstalk” the Millimeter Forum.
