Prevising the Vision
Apart from the actor's performances, almost all of "Gravity" was accomplished with a
seamless fusion of CGI and computer animation, requiring the total orchestration of man and
Production began with a process called previs -- short for previsualization -- wherein the
entire movie was meticulously mapped out in the computer, encompassing everything from
blocking, to camera angles and lighting, to design.
Visual effects supervisor Tim Webber says, "Previs can be very basic, but on 'Gravity,'
we went much farther down the line. We needed to work out all the shots in great detail
because so much was going to be computer-animated -- the notable difference being that the CG-animated portions had to look completely photo-real. It's not a cartoon and not a sci-fi
fantasy; everything had to feel like real life, so we needed to have a precise idea of how it was
all going to look and move together. We mostly used keyframe animation for the characters and
camera, but we also gave Alfonso a camera and he was able to watch a virtual picture on the
screen. As he moved around, he could frame the shots and plot all the action of the movie."
Cuaron confirms, "We didn't have the usual freedom of animation, as we had live-action
elements that had to blend with the animation, and the live action was limited by what was
preprogrammed in the previs. Tim tried to give us as much flexibility as possible, but most
often, once we had made a commitment, that was it. Due to the technological process, the
margin for improvisation and spontaneity was very small, which added to the challenge for
Sandra and George. But watching their performances, no one will feel the limitations placed on
them, and that is a testament to what amazing actors they are."
Senior animation supervisor David Shirk and animation supervisor Max Solomon and
their department were also faced with the juxtaposition of live action and computer animation,
adding in the rules of zero gravity, where what goes up doesn't ever come down. "We had to
relearn physics since we were all used to motion arcs that are determined by weight," Shirk
remarks. "We had to forget all that and assume, for instance, if something is spinning, it will
keep spinning forever until it interacts with something that changes that spin."
"In outer space, there is no up, there is no down," states Cuaron. "It took a lot of
education for the animators to fully grasp that the usual laws of cause and effect didn't apply. It
was a learning curve for all of us."
One learning tool that the animators used was called a ragdoll simulation because, as
Solomon explains, "it's basically a floppy character that we could throw in virtual space and it
simulated how a body might move. It was quite useful to get people's heads around how a
character would fly. Where it was not useful was that people aren't ragdolls; they have arms
and legs that react to things," he smiles.
During the previs phase, Cuaron and cinematographer Emmanuel Lubezki could also
establish the extended shots that have become a signature of the director -- a prime example
being the opening sequence that introduces Ryan Stone and Matt Kowalski against the
magnificent vista of space.
"From the beginning," says Lubezki, "Alfonso wanted to do very long, continuous shots,
which is something we have had success with on other films, but 'Gravity' was the first time I'd
be doing virtual photography. With the substantial amount of CG, we found we could take that
approach to the extreme. It allowed us to do what we called 'elastic shots,' where we went from an objective wide view to an extreme close-up of Sandra's face, and then into her helmet to a
subjective POV angle and then back out again to a more objective shot. It gives the audience
that feeling of claustrophobia and a better understanding of what the character is going
Webber adds, "Alfonso made good use of the camera's capability to float around, rotate
and spin in a virtual environment. Characters could roll upside down and the camera could go
above, below or around them. In particular, when you have those extended shots, it meant you
could keep everything going very fluidly and there was plenty of opportunity for uncommon
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