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The Prevalence of Previs

Vfx professionals discuss with Janet Hetherington how previs is becoming more widely integrated into the production process.

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Bill Westenhofer, vfx supervisor of The Chronicles of Narnia, finds that previs allows vfx departments to be more precise in pre-production. © Disney Enterprises Inc. and Walden Media Llc. All rights reserved.

Todays previsualization techniques are tending to look more and more like the actual end product. And in the current vfx environment, previs often acts as a digital blueprint, allowing filmmakers to plan a movie in incredibly accurate detail.

Its all there in the previs, and it is simply a matter of extracting the information needed, says Ron Frankel, president of Proof Inc. (September and Charlottes Web). In the context of complex sequence that involves multiple departments and filmmaking techniqueslive action, CGI, miniatures, stunts, special effects, etc.using previs brings an added level of confidence, focus and efficiency to the production, which all translates into less waste and a better product.

Previs has definitely become an integral part of vfx and is increasingly common in the wider filmmaking process, adds Paul Franklin, head of 3D, Double Negative (Flyboys and The Da Vinci Code). From a purely financial point of view, previs can really help lock down shot costs as it gives you a sneak peek at what you are getting into well before you start spending all the money. This alone makes previs very attractive to producers who are keen to keep the budget under control.

Todays films are often requiring more and more effects shots, agrees Bill Westenhofer of Rhythm & Hues (The Chronicles of Narnia: The Lion, the Witch and the Wardrobe). Budgets, however, seem hesitant to follow suit. As a result, the need for a production to have a good understanding up front of exactly what is in store is getting very important. This is a place where quality previs is incredibly useful. Directors who are not vfx savvy can become more comfortable with what is in store for them. Additionally, previs allows vfx departments to be more precise in what is expected for each shot, which allows more precise planning for the shoot, and thus tighter up-front bids.

In fact, previs is now being built up-front into budgets. As more productions make use of previs and see how helpful it can be they are starting to include time in the schedule and money in the budget for previs, asserts Frankel. There is still an interesting debate between using independent previs, like Proof, or getting previs from the final visual effects vendor. Not surprisingly, I advocate independent previs because I believe you get more value for the money spent. But in either case, a good previs team accurately represents the directors vision, can help answer difficult questions and can help a production run more efficiently.

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Andrew Jones, cto for Pixel Liberation Front (Superman Returns), says, We are doing a lot more work to visualize the look and feel of the projects we are working on. When people watch our more recent previs, they typically have a much more emotional response than they did in the past. In the technical arena, there have also been several leaps forward recently toward using the tools from previs to enhance the actual shooting. For example, on motion-capture sets, it is now possible to look at a live retargeted CG character being driven by an actor on the stage. As that sort of technology takes hold, previs is becoming an even more important tool for preparing the digital assets and sets that will be needed later in the process of making a film.

Previs Process

Making wider use of previs has even caused changes in the production process from beginning to middle to end.

Most significantly, [previs] now functions across practically every department within a film production, observes Frankel. We can spend as much time working with the production designer as we do with the vfx supervisor. And we certainly arent strangers to the director of photography, special effects or the grips. We are also doing more work during development and pre-preproduction providing exciting animatics to help sell ideas to the studio or to justify an increase in a films budget.

Frankel points to the current Oliver Stone film, September, as an example of how previs is being integrated into the production process. Previs has been the focal point of ongoing discussions involving Oliver Stone, the production designer (Jan Roelfs) and visual effects supervisor (John Scheele), Frankel explains. The discussion will start with Stones description of a shot, which I will mock up in the 3D environment. Everyone will look at the composition and make refinements until it meets the directors approval. At that point, the discussion turns to the question of how will the shot be executed: how much will be practical location or set and how much will be visual effects set extension?

Inside the previs environment, Ill move the boundary between practical and CGI back and forth until we ultimately reach a solution that is feasible within the schedules and budgets of both the art department and visual effects. Once the boundary is settled, the rigging grips join the conversation to discuss how much bluescreen is required and where it will be positioned, and often the ad comes in to get a preview of how the set is going to look. In this film there are a large number of extras so the ad will often ask for changes to accommodate the extras moving in and out of frame, and if those changes effect the bluescreens or the CGI/practical boundary, then the changes filter all the way back up the chain for approval.

Previs has definitely become an integral part of vfx and is increasingly common in the wider filmmaking process, observes Paul Franklin, who is working on The Da Vinci Code. © 2006 Columbia Pictures Industries Inc. All rights reserved.

Previs has definitely become an integral part of vfx and is increasingly common in the wider filmmaking process, observes Paul Franklin, who is working on The Da Vinci Code. © 2006 Columbia Pictures Industries Inc. All rights reserved.

This work is all done prior to filming so there is plenty of time to address everyones concerns and arrive at a solution that ensures the fewest number of costly and slow on-set changes.

Frankel says previs also helps everyone get on the same page visually. On Pirates of the Caribbean 2 & 3, the previs has played a vital role in communicating director Gore Verbinskis vision to the various departments, Frankel adds. The previs team works closely with Verbinski, visual effects supervisor Charlie Gibson and editorial to create sequences that have the right pace, energy and excitement. The approved sequences are distributed to the various departments so they can understand what is expected of them and begin planning how they are going to accomplish each shot. The previs has been particularly useful to stunts to help rehearse their moves.

Ron Frankel, president of Proof Inc., says previs helps everyone get on the same page visually. It plays a vital role in communications between the director, vfx team, editorial and production designer.

Ron Frankel, president of Proof Inc., says previs helps everyone get on the same page visually. It plays a vital role in communications between the director, vfx team, editorial and production designer.

Frankel maintains that work on Charlottes Web presented a new challenge to Proofs previs team. At first glance, the project seemed fairly typicaldesign sequences and break them down into which elements are practical and which are CGI. This remained a huge part of the project, but we quickly became engaged in purely creative issues, such as how to frame a two-shot between a spider and a pig, or worse a spider and horse! Also, since so much of the film takes place inside the barn, with the animals inside their pens, how do you keep the film dynamic and not end up feeling like youre watching a bunch of animals in their pens inside a barn?

To resolve those issues, Frankel says that for Charlottes Web, the previs was approached as if the film were an animated feature, with editorial constructing a complete story reel composed of drawn storyboards and previs animatics. Scratch dialogue was laid on top with music and basic sound effects. On all of these films, previs has proved to be an indispensable tool: a quick, cost-effective way to lay out the creative vision of the film and follow that up with tangible information that helps the various departments accomplish what is needed to translate that vision onto film quickly and efficiently.

For Flyboys, Franklin says Double Negative created some 25 minutes of previs. The full range of modern previs techniques were employed to create extensive animations, comprising hundreds of shots depicting complex aerial battles between biplanes in the First World War, Franklin explains. The previs was then used as a bible for how the final work in the movie ended up looking. Franklin adds that one of the differences with Flyboys was that the latest software and hardware tools allow far more to be generated in a much shorter space of time. This, in turn, means that the editorial department can be supplied with enough material to quickly cut whole sequences together, rather than just insert a few isolated vfx moments.

In addition, Double Negative has been using previs to crack film challenges posed by The Da Vinci Code. It proved to be a very quick and effective method for developing the look and feel of complex live-action sequences, Franklin says. The ability to generate sequences of creative camera moves in rapid succession was critical in locking down the on set requirements, and helped to give the best possible result within the available limits of the shoot. One crucial aspect of the process was the ability to take camera moves designed in previs and export them to a motion-control camera system for on-set photography.

Postvis was used on Charlie and the Chocolate Factory. Nic Hatch explains that some shot sequences lacked the vfx needed, so he and his team would quickly insert the visual effect. Courtesy of Warner Bros. Pictures.

Postvis was used on Charlie and the Chocolate Factory. Nic Hatch explains that some shot sequences lacked the vfx needed, so he and his team would quickly insert the visual effect. Courtesy of Warner Bros. Pictures.

Previs and Postvis

Movies are also making use of previs much later during post-production, hence the term postvis. On Charlie and the Chocolate Factory, there were a few sequences that had been shot, but lacked the vfx needed to aid in the telling of the story, explains previs supervisor Nic Hatch. Wed very quickly gather the dailies from editorial, rough-track the plate, if necessary, and insert the visual effect, be it Gloop in the river being sucked up the pipe, or Violet turning into a blueberry. Where this really helps the editor and director, and ultimately everyone else involved, is in the pinning down of what the shot and sequences require to make them work as a piece of narrative. Often post-production houses are not geared up or able to complete the postvis work quickly and efficiently, as they are more intent on, and quite rightly so, finishing work to a finite polish, which will always take longer and require a different skill set.

At Double Negative, postvis is utilized when very basic temp comps are made, often using telecine rushes of principle photography. As digital editing systems become more and more sophisticated, a lot of this can actually be accomplished in the editorial department, Franklin explains. If you have planned your previs pipeline effectively you can use the elements and layers created by the previs team in combination with the rushes to produce simple temps of shots that serve as much more than placeholders in the cut.

On King Kong, postvis was used most often when they had to integrate live-action elements (usually involving actors) that were reshot by Peter Jackson, thus altering the previs. This included the landing of the Venture ship on Skull Island, many of the Skull Island scenes and during Kongs rampage of New York.

Our initial phase of previs was sitting down with Peter and talking loosely about ideas and then the animators would come up with gags themselves, explains previs supervisor/animation director Christian Rivers. Wed review those as little animations and hed tell us what he liked and didnt like. It was a much bigger collaborative process [than on Lord of the Rings]. What happens is, when you animate a sequence, it has an eye of God chronology. But well cover that with 15 or 20 cameras, which gives him a huge array of footage. So it starts very complete with these 3D scenes and hell edit and it will become a huge mix of images that arent tied to any chronology. And thats fine if its a montage, where we can get away with those jumps in continuity, but [not so fine] where youre combining vignettes with Kong picking up a dino here and throwing it from another vignette. Unfortunately, all the mundane logistical things that we need locked down as 3D artists for environments and animating our creatures goes out the window. So thats where postvis is very handy: where we go back in again after Peter has edited footage and make that feel cohesive and in practical terms give it a consistency and continuity. If he changes angles, we rebuild the previs scene so we can pass that off to Weta Digital.

On King Kong, postvis was strategically used when they had to integrate live-action elements involving actors that were reshot by Peter Jackson, thus altering the previs © 2005 Universal Studios.

On King Kong, postvis was strategically used when they had to integrate live-action elements involving actors that were reshot by Peter Jackson, thus altering the previs © 2005 Universal Studios.

In the very sense of the words themselves, previs would naturally fit at the front of a production, while postvis follows at the end. However, those boundaries and functions are getting blurred.

Persistance of Vision (POV), which recently completed work on Mission: Impossible 3 and is currently working on Journey to the Center of the Earth 3-D and Eragon, offers postvis as part of its arsenal of services. This entails video footage of the live-action photography to integrate the rough visual effects elements with the actual filmed material, rather than being all-digital or all virtually in-camera. First heavily used by David Dozoretzs previs team for Star Wars: Episode I The Phantom Menace, postvis allowed George Lucas to edit the film shots in various stages of completion: previs, postvis, non-effects shots (of which there were few) and ILMs finals.

Some sequences are never prevised, but only postvised, adds Dozoretz, who heads up POV. Postvis artists must do everything an entire pipeline does at low-resolution, including camera tracking, animation, matte work, lighting, rendering and compositing.

Frankel says that Proof has been involved in a number of productions where they have transitioned from previs to postvis, often with a short hiatus between the two, Postvis functions similarly to previs in that it keeps the creative decision-making centralized within the production, rather than dispersed among several visual effects facilities. On a film like Fantastic Four, the Proof postvis team was located within the vfx office and adjacent to editorial. We were able to make quick temps of vfx shots and get them back to editorial so they could review and make decisions on which shots to release to the vendors. In order to make accurate temps, we worked closely with the vfx vendors, making sure our shots were in keeping with what they planned on delivering as final CGI.

Todays previsualization techniques are even finding a new role performing postvisualization functions. One interesting way that previs can be used is actually after the live-action shoot is done, suggests Rhythm & Hues Westenhofer.

One of the challenges in editing a film with a lot of CGI characters is that its hard to cut a scene with a lot of blank plates. On Narnia, the character previs that was done was output over blue and used by the editorial staff as an animation stand in to help this process. This allowed for the turnover of tighter cuts, which resulted in less cut changes after real animation was underway.

Janet Hetherington is a freelance writer and cartoonist living in Ottawa, Canada. She shares a studio with artist Ronn Sutton and a ginger cat, Heidi.

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