On Iron Man, Favreau used previs as a medium to experiment and a way to get ideas evaluated. For him, previs was a “template,” but not the movie itself.

Seki suggests that Favreau’s approach to previs was a bit unconventional. He used it as a medium to experiment and get as many ideas out and evaluated as possible. He was adamant that the previs was a “template,” but not the movie itself. ILM Animation Supervisor Hal Hickel once speculated, according to Seki, that Favreau’s acting background and his penchant for improvisation may have been the source of this process.

"The notion of continually revising and improving sequences can be a bit daunting; however, if the environment in which you work is supportive and collaborative, as it was with Iron Man, you find yourself embracing the process. It can be infectious. John Nelson seized upon this notion. ILM VFX Supervisor Ben Snow and Hickel would be involved in brainstorming sessions alongside Storyboard Artist David Lowery and our previs team. I enjoyed trading ideas with the final [vfx] vendors with whom you normally have very little interaction.

"As a result of the open approach, repurposing little beats and character vignettes became more common place. For example, an early version of Gulmira had the beat where a militant comes up behind Iron Man with a handgun only to have the bullet ricochet off Iron Man’s helmet, killing the gunman. Even after the filmmakers scrapped that version of Gulmira, Second Unit Director Phil Neilson decided to film the ricochet moment during Tony’s escape from the cave. That beat got a lot of laughs when I saw it. The Orphanage submitted an early test to the production during bidding of Iron Man in which he stands off against a tank. That bit became the cornerstone of the Gulmira sequence. In fact, when we prevised Gulmira, we just slugged in their test for that portion of it. I think the vendors really embraced this notion of collaboration. It could have been extremely politicized and difficult, but because the players were on board and open-minded, everyone 'played nice' in the sandbox."

Unlike Iron Man, the previs for Speed Racer was far more complex and divided among several companies: Digital Domain, Halon, PLF and Proof. As has already been thoroughly documented on VFXWorld, Speed Racer offered an innovative artistic experience, combining a new 2.5D live-action anime look called "Photo Anime" that carried over to the immersive car racing/fighting called "Car Fu."

Previs was used as a conceptual design driving force as well as a shot and sequence design tool. All Speed Racer images from Halon and courtesy of Warner Bros.

Alex Vegh of Proof was the initial previs supervisor, who worked in L.A. during concept design and early production work. He briefly worked in Berlin too, which is where the production was based. Vegh suggests that the design of Speed Racer truly pushed the boundaries of previs. "Generally, previs is used to plan how a sequence is played out or how a tricky shot is executed," Vegh explains. "The Wachowski brothers' creative vision not only challenged the traditional look and feel of previs but also its usage. Previs on Speed Racer was used as a conceptual design driving force as well as a shot and sequence design tool.

"We had a unique opportunity to do conceptual design before kicking into a pre-production/shot planning phase. The inspiration for the look and feel of the film reached out to everything from classic anime and arcade videogames to fine art photography and QuickTime vr [virtual reality] bubbles. Throughout the development process the previs team created several proof of concepts about the racetracks, the cars and the environments.

They used QuickTime vr bubbles to create the worlds the characters and cars lived in. These were executed mostly by Christov Effects and Design, under the guidance of owner Lubo Histrov, the visual effects environments art director, and leader of the in-house World Team stills department. "The idea is that one takes several high-res images from one location rotating the camera until 360 degrees of image in all directions is captured," Vegh continues. "From there the individual images are stitched together and projected on a sphere. This allows a virtual camera inside the sphere to rotate freely and translate slightly without distortion to the image projected on the sphere giving the illusion that a foreground greenscreen element is an integral part of the background. We took this idea and pushed it to the limit seeing what would happen if you distorted the sphere or intentionally got too close to the edge of the sphere with some very interesting results. Another benefit of using this technique is a camera can travel from one bubble or environment to another seamlessly like an actor traveling from one room to another. This bubble concept was meant to be the basis for how the location photography was to be done."