How does an Earthbound filmmaker create -- and sustain for a white-knuckled 91 minutes -- what astronauts experience in space? To meet that daunting challenge in Gravity, which just opened to $84.2 million worldwide, director Alfonso Cuaron and his collaborators remastered the laws of physics and created a whole new lighting system.
STEP 1: Simulating Weightlessness
Despite all the apparent photo-realism of shots of Sandra Bullock and George Clooney drifting in the void, 80 percent of the film was hand-animated on a computer, right down to the clear visors in front of the actors' faces. To do that, animators -- many of whom have spent their careers giving CG characters and objects the illusion of weight -- had to throw out everything they'd learned.
"We had little physics lectures to explain to the team how things work -- not just in zero gravity, but because there is no air, there is no air resistance. Once something starts moving, it doesn't slow down as it would on Earth," explains VFX supervisor Tim Webber of London's Framestore, which handled the majority of the visual effects on the $100 million movie.
STEP 2: Capturing the Light
Because light behaves differently in space, director of photography Emmanuel Lubezki and the VFX team collected information from NASA to plan how to re-create it on film. "In orbit, a whole day is 90 minutes," says Webber. "So a whole day of lighting changes every 90 minutes. We used sunset, moonlight, strong daylight and being in the shadow of the Hubble at times. And we made sure the quality of light was rich and varied; when they were over the ocean, there were cool blue lights, and over North Africa there were warmer colors coming from the desert."
To make sure the light on the actors' faces matched the virtual light that already had been programmed into the CG shots, the actors were filmed using an Arri Alexa camera in a specially designed "light box": a 20-by-10-foot cube lined with 196 2-by-2-foot panels fitted with 4,096 lights. "The LED lights were all separately controllable," says Webber, "and they would project light on the actors' faces and give them the idea of the environment they were in."
STEP 3: Performing Acrobatics
To capture close-ups of Bullock, which were added to the CG shots of her character tumbling head over heels, cameras were placed on a motion-control rig. And the production came up with a new device: a 12-wire rig with a carbon-fiber harness, which, Webber says, gave the filmmakers the ability to "completely puppeteer Sandra."
STEP 4: Adding Depth
Cuaron chose to work in 3D for the first time so he could create a greater sense of the depth of space than 2D could suggest. His goal, he says, was "realistic 3D, the way that your eyes would see it." The CG portions of the film were created in 3D on the computer, while the live-action shots were filmed in 2D then converted to 3D.
STEP 5: Laying in Sound
Even though sound doesn't travel through space, supervising sound editor and designer Glenn Freemantle felt the audience should hear the sounds that travel through vibrations and touch. "When [Bullock] is in the suit, you hear her voice and her breathing, and you hear through her suit when she is in contact with things," he explains. His team captured sounds by recording with contact mics at car plants and hospitals. "We even recorded through water with a [submerged] guitar," he recalls.
While Gravity builds on VFX techniques in movies like Avatar, it points toward a future where actors will perform on more advanced virtual soundstages. "This is a step toward shooting movies on the 'holodeck,' " says Paul Debevec, associate director of graphics research at USC's Institute for Creative Technologies and a consultant on Gravity.
"Eventually we are going to have a great virtual environment that is three-dimensional and believable. Instead of putting actors on a green screen, you'll film them on an enormous, enveloping 3D display, and the director and cinematographer will have complete control."