Another fiscal use of previs is for budgeting VFX shots. “For instance, if a producer from X-Men had gone to an FX house and said, ‘Give me a quick quote for a shot of Sir Ian McKellen walking through a giant chasm on metal plates with all kinds of things flying around and with a waterfall in the background,’ they would either ask him, ‘Are you crazy?’ or give him some huge quote,” notes Cranford. “Instead, the producer was able to take a previs shot with all the elements laid out, including camera angles, and get a reasonable quote in a reasonable amount of time.”

A 3D model of the submarine in K-19 was completed in two weeks by Keyframe.

“This film is a cross between Red October and …”
Cranford notes that the demands for modern previs are very exacting. “These are not very crude animatics scenes,” he says. “They’re more like the high-res cinematics of a video game. One scene can easily have half a million polys in it, complete with 3D sets, detailed backgrounds and multiple moving vehicles and actors.” This explains why previs is such a recent occurrence —10 years ago, the 3D animation tools and computer power for quick creation and fast rendering of detailed scenes simply did not exist. On the positive side, it means that previs scenes are actually clean enough that they can be used to pitch the movie to the studio in the first place. “A crew had been working for some time to build a set to take test shots for K-19: The Widowmaker, but it was very time consuming,” he notes. “We created a complete 3D model of the submarine in about two weeks, and inserted characters who walked through the entire virtual set. The resulting scenes were good enough that the producer used them to pitch the studio, and that got it greenlighted.” Using previs scenes to pitch a studio is no longer unusual — even a megaproject such as The Lord of the Rings trilogy used previs scenes extensively to get its $300 million budget approved by New Line Cinema. This gives you an idea of how much of a film can be affected by previs — from the initial funding through pre-production through filming, and finally leading into post-production VFX and DAM (digital asset management). The tie-ins with asset management are especially important for films such as the Matrix franchise, where digital assets from the first film are re-used both for sequels and for gaming spinoffs.

Keyframe Digital Prods., co-founded by Darren Cranford, has executed previs work for such features as Driven, Exit Wounds and Bulletproof Monk. Photo credit: Chris Chew.

A skilled previs supervisor must be both technician and artist — it is the ability of the previs to convey both the movement and feel of the story that enables it to be a critical common portal for the many communities of practice that work on a film — including the director and AD, the designers, the set builders, the actors, the producers, the grips, even the musicians creating the score, all of which would normally have a hard time “reading from the same page.” The extensive use of previs in a film means that the previs supervisor and his animation production team will spend a lot of time with a film. “For X-Men, we spent over seven months on the film, and created hundreds of shots and over 45 minutes of 3D animation,” remarks Cranford.

“What if we moved it just a little…”
A major role of previs is precise virtual camera placement, and this is one area where directors will brook no compromise. “If the director says, ‘I want to put a camera with a 22mm lens one foot from the wall and 10 feet up in the air,’ that’s exactly what we have to give him,” notes Cranford. “And if he then wants to do ‘what-if’ explorations, such as, ‘What if we made it a 50mm lens?’ we have to provide him with that look, and soon. Directors are people who like instant gratification. It can get very exacting — for the movie Driven we had to build a virtual racetrack with stands and 14 cameras, and change any and all of the cameras and lenses on a given day.”

Cranford relies on 3ds max for enabling him to build precise 3D sets and set up virtual cameras with lenses that are exactly correct. For moving characters and vehicles around, he likes the easy-to-use features of the Character Studio plug-in for max. “I use max extensively, along with combustion, which is a great compositing tool. What we typically do first is create the set, using data from the film’s technical survey group, which hopefully includes blueprints of buildings and rooms and terrain features and elevations. Sometimes we have to go out to the location ourselves, with measuring tools. We take lots of digital photos, which we then use as textured wallpaper for the 3D sets. We also have to pay special attention to light sources.”