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Previs Glossary
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The ASC, the Art Directors Guild and the Visual Effects Society join forces to explore the existing and potential uses of previsualization.

Images courtesy of The Third Floor and Pixel Liberation Front
Previsualization is the process of using computer-generated animation to explore scenes and sequences before they are shot, and it can significantly impact the cinematographer’s job. It can enable the director of photography to become even more involved in shaping a movie’s narrative; conversely, there is a danger he or she will end up merely executing shots that were conceived and detailed by someone else long before the cinematographer joined the production. “I can understand why cinematographers have been reluctant to embrace previs: they’re often excluded from the process,” says Chris Edwards of The Third Floor, a company specializing in previsualization. “But we have found their involvement is really key.”

To address some issues related to previsualization, including how best to integrate it into production, the ASC Technology Committee recently joined with the Art Directors Guild and the Visual Effects Society to form the Previsualization Committee, the first joint committee formed by the three organizations. Co-chaired by Ron Frankel, the owner of previs company Proof, and David Morin, a consultant with Autodesk, the group began meeting in April 2008. Over the course of 12 meetings, it has brought together some of the leading previs practitioners in the industry, cinematographers, production designers, visual-effects supervisors and other filmmakers to explore previs and the role it should play in the future. “Learning how other people see this process has been very insightful,” says Frankel. “Previs is coming into its own in a very interesting way.”

Previsualization has been around in various forms for decades. Before shooting the original Star Wars, George Lucas worked out the timing for space battles by cutting together footage of World War II fighter-plane dogfights. On the third Star Wars film, Return of the Jedi, the speeder-bike sequence in the forest was tested out using action figures that were shot with lipstick cameras. “We could figure out movements and work out a little, dynamic piece of action, then cut it together and see if the shots we’d planned were going to work well,” says Neil Krepela, ASC, a cinematographer and visual-effects supervisor who worked on Jedi.

In the definition crafted by the Previsualization Committee, previs generally comprises computer-generated imagery created in a 3-D modeling-and-animation application and then edited together to demonstrate the potential execution of a scene or sequence. According to the committee’s research, the earliest example of CG previs appears to be The Boy Who Could Fly (1985). During a sequence in that movie, two children fly over a school fair filled with amusement-park rides; the child performers were held aloft on wires suspended from a large crane, and the sequence was covered with a Skycam supported by pylons. James Bissell, the project’s production designer and second-unit director, asked Canadian computer-graphics company Omnibus to help him create a digital version of the sequence so he could experiment. The resultant previs enabled him to see where the shadows would be at different times of day so he could position the camera and crane as efficiently as possible. “They said, ‘What a great use for the technology — we never thought of that,’” recalls Bissell. “It allowed us to shoot a pretty elaborate sequence in about three days.”

Previs is not visual effects, although the two disciplines are often lumped together, perhaps because previs is commonly used on pictures that involve complex visual-effects sequences. Also, many of the tools and applications used in previs, such as Maya, are also used for visual-effects work. But previs is as different from visual effects as a sketch is from a painting; it’s about quickly trying out possible shots and sequences in real time and making changes on the fly, rather than making polished shots that are textured and properly lit. “Previs is used to tell the story in the rawest possible form,” says Laurent Lavigne, whose previs work includes the films Transformers, Jumper and The Last Samurai.

Contrary to popular belief, previs is not an entry-level visual-effects job. “I believe it’s a specialized field that requires classically trained artists,” says Steven Yamamoto, whose previs credits include Public Enemies, Hancock and The Sorcerer’s Apprentice. “You need a high level of knowledge of not only CG work, but also creative storytelling. Combining those skills is asking a lot of one person.”

The previsualization process begins with the creation of digital assets: sets, characters, vehicles and anything else that needs to be modeled in CG. These elements are then animated, and actions and positions are set, just as a director would block a live-action scene with real actors. Next, virtual cameras are placed into the scene. Angles, lenses and moves are chosen, and shots that cover the action are rendered out. These shots can then be assembled into a sequence or handed to the project’s picture editor, who adds them to the cut as though they are real coverage. Previs can be continued on set, to solve problems and validate what’s been shot, and in post, where previs elements can be retimed and adjusted to fit with the real footage as it becomes available.

Companies considering the use of previsualization should know up front what they need and want from the process. It involves a variety of logistical questions, some of which can only be answered on a project-by-project basis: How should the previs crew be structured? Is it best to have a team of artists from one company, or should the team comprise several artists who are independent of one another? Once a team is in place, to whom should they report? Which departments should be involved in the previs process? Should the team work in its own office or on-site with the project’s crew or production staff?

The biggest previs question might be: Who is it for, and what is its purpose? Some people see the process as a way to work through logistically difficult sequences, determine what will be necessary to shoot them, and then provide the relevant departments with very precise data. Roberto Schaefer, ASC says that on Quantum of Solace, previs was used for very technical reasons: “We did a lot of previs for set construction; they built CG sets to make sure we could get the angles we needed. The scaffold-and-rope fight scene was a complicated jigsaw puzzle because the set didn’t fit into the stage — it hit the rafters and was supposed to be 20 feet taller than
it was. We wanted to do a previs to make sure we were on the same page for camera angles, movements and so on.” Others might see previs as a tool for exploring the narrative. “The animation pipeline has a story department, but live action doesn’t, and previs becomes the ersatz story department,” observes David Dozoretz of Persistence of Vision.

Working with a small number of digital artists — sometimes just one — gives a director a relatively inexpensive, low-pressure way to explore ideas, and it’s easy to discard any that don’t work. “Previs is the director’s ‘undo’ button,” says Edwards. “In film school, I learned that every moment I waste is a moment I’m sucking out of my movie. If you’re going to make mistakes — and you will — it’s better to do it with a smaller team, and you’ll probably make fewer mistakes.” Colin Green of The Pixel Liberation Front adds, “If filmmaking is about real heat-of-battle decision-making, previs allows for decisions to be made with more deliberation. We force answers to creative questions and make contributions to the creative vision. The formalism of the medium forces you to figure things out in a way that storyboards and finger gestures never will.”

The perception of previsualization as a time to experiment raises still more questions, including how finished previs materials should be. One topic of discussion in the Previsualization Committee has been whether the CG models made in previs can or should be constructed in such a way that they can later be handed off to a visual-effects facility and used as the basis for the final effects. “There’s always someone who believes he can set up this amazing pipeline and integrate previs and effects, but right now, you can’t do that,” notes Nic Hatch, owner of London previs facility Nvisage.

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