The Digital Rehearsal
Previs (or previsualization, sometimes spelled ‘previz’) is a sophisticated filmmaking technique that uses 3D computer graphics to create a detailed, animated mock-up of a scene or sequence before filming begins. It goes a step beyond storyboards and animatics by creating a virtual, three-dimensional environment that mirrors the real-world set or location. Within this virtual space, filmmakers can place digital stand-ins for actors, props, and set pieces, and then experiment with virtual cameras that have the exact properties (lens, movement capabilities) of the real cameras that will be used on set.
This ‘digital rehearsal’ allows the director and cinematographer to design and block out complex sequences with incredible precision. They can test different camera angles, lens choices, and intricate camera movements—like a sweeping crane shot or a fast-paced dolly move—to see exactly how they will look. For action scenes involving stunts, vehicle chases, or large-scale destruction, previs is invaluable. It allows the filmmakers to choreograph the action safely in a virtual space, ensuring that when the real, expensive, and often dangerous stunt is performed on set, everyone knows exactly what needs to happen and how it will be filmed. Directors like James Cameron (Avatar) and the Russo brothers (Avengers: Endgame) have used extensive previs to plan their massive, effects-laden set pieces.
From Previs to Postvis
The utility of previs doesn’t end when filming begins. The data generated during the previs process—such as camera positions, movement speeds, and lens information—can be exported and used to control motion-control camera rigs on set, allowing for the perfect replication of the planned virtual shot in the real world. This is especially crucial for visual effects shots, where the live-action plate must match the digital elements perfectly.
After filming, the process can evolve into postvisualization (or ‘postvis’). In postvis, the newly shot live-action footage is composited into the rough 3D previs animation. This gives the editor and director an immediate, albeit crude, version of the final visual effects shot, allowing them to edit the scene with the correct timing and framing for the yet-to-be-created digital elements. It helps answer questions like, ‘Is the shot long enough for the dragon to fly past?’ or ‘Does the timing of this explosion work with the actor’s reaction?’ This continuous loop of visualization, from previs to production to postvis, creates a highly efficient and creatively flexible workflow for modern, blockbuster filmmaking.