Proof’s Previs & Postvis Charts the Galaxy for Marvel’s Guardians

Production VXF supervisorStephane Ceretti, who worked with the Proof teams both in London and Los Angeles, described developing the sequences early in preproduction with the director, Proof’s previs supervisorEarl Hibbert, and the storyboard artists.  

Fast Paced Shoot

“We wanted to be as prepared as possible for a fairly complex and fast paced shoot,” Stephane said. “Earl and his team collected all the necessary information from James, the Art Department and VFX department, and came up with previs that really made sense and made a big difference in the way we prepped and shot the movie. All of the main sequences were previsualized before we started shooting, which allowed each department to get a visual sense of the film and what they had to achieve during the shoot. It was an essential tool for the VFX vendors as well.”

Earl Hibbert said, “James always came prepared with storyboards or a shot list and thumbnails that he'd use to pitch to us what he was looking for in the sequences. Once we blocked in the action with him, he'd explore the camera and character blocking ideas with us, to refine where he was going with an idea.
 
“The production designerCharlie Woodand the Art Department were ready to supply us with the building plans for any sets, ships and vehicles they were working on. We'd take their 3D models and down-res them to match our previs requirements. We could then turn around and supply any techvis they needed for the shoot. Because this was a complicated project, we made it a collaborative effort on all fronts and worked together to get the job done.”

The Virtual Set

The production involved a lot of green screen work and most sets were built from scratch, which meant the team had to make sure that the action they designed during previs would fit into the sets that were under construction. Consequently, Proof followed the work of both Charlie Wood and Stephane Ceretti very accurately to make sure the dimensions of their virtual set would match the actual build.

Lead Compositor at Proof,Theresa Rygielsaid, “In a few instances during postvis, we had no information other than Stephane Ceretti’s memory and imagination to help build the virtual sets. We worked with Steph sitting right there at the computer, armed with a basic floor plan and some select photos of similar environments for shape and lighting. He would think about how the action would progress while we covered the digital ground with him to keep the action flowing and interesting.

“It was amazing to work so quickly and creatively while keeping in mind scale and points of interaction. The live-action photography of our sequences took place on a single green screen stage, but once each shot was composited into its specific place in the virtual environment, the sequence played out like a travelling battle.”

Connector Shots

An important issue for James, Stephane and Earl was seeing the intense action in this movie through the audience’s eyes. Earl said, “We never wanted the audience to get lost in any of the action scenes or lose track at any time of where they were in the space of any big action moment. We often built ‘connector shots’ into the previs, so once a big action moment happened, or if our characters changed positions, we would always build in an interesting and dynamic wide shot to tell the audience what direction we're travelling, where our heroes are and where our bad guys end up. So, when we cut back in close to one of our heroes, the audience always knew who they were with and not be confused.”

They sometimes used this POV style of camera work in creative ways as well. For example, in the final battle sequence, they might stage the battle action on a diagonal axis, rather than on a level. “We felt it would add an extra layer of anxiety and danger for our heroes, who have to fight their way up to the Dark Aster - a three-mile long warship. That slight shift in perspective had a huge impact on the feel of the sequence. Rather than two forces colliding on an open plain, we constructed a ‘hillside’ style of attack where the bad guys controlled the higher ground,” Earl said.

Rocket and Groot

A special task the Proof team faced on this film was helping to bring to life the all-CG characters Rocket, a feisty racoon, and Groot, a great walking, almost talking tree. James particularly wanted the audience to forget that these two heroes were digital and, because they are at the heart of the story, to accept them as real characters that actually exist in the world of the film.

Ron Frankel, Proof’s founder and creative director, said, “One of our biggest challenges for this film was making sure that Rocket and Groot developed into compelling characters that the audience found believable. Because the goal was for the three companies - MPC, Framestore and Proof – to share assets, it was extremely important that we all started from the same point.

Framestore and MPC were charged with the initial visual development of the characters and did the first animation work that started to define their personalities, while the Proof team made sure that the previs versions of Rocket and Groot matched what was coming out of their offices. Proof’s TDAnna Leewrote a real-time CGFX fur shader so that our model of Rocket would appear furry and have the same volume that the final character would have.”

Earl Hibbert noted that working with Rocket and Groot was both a challenge and lot of fun. “The fun aspect was discovering their personalities with the director,” he said. “He had very specific ideas about how they would move and interact with our heroes throughout the movie. A lot of the Rocket and Groot gags we developed with James in previs and postvis ended up in the final movie - a testament both to James’ vision and to the Proof team’s ability to deliver on it.”

Technical Coordination

One of their more complicated postvis sequences came near the beginning of the film when Groot and Rocket are trying to trap Gamora, another of the Guardians. “While Rocket is wrapped around her neck,” Theresa said, “Groot's limbs are stretching and growing around her waist and legs. Everything - from the actor's performance with a stunt person in green, to rigging and animating Groot vines, to compositing three characters' body parts wrestling, motion blurring and deciding what gets roto'd in front of what – it was all a real challenge.

Mapping Interaction

The Kyln escape also features the moment when Groot grows his bark into a shield to block bullets, a scene they worked on carefully with James to define the basic shape of the shield and how Groot would use it to protect himself and Rocket. In the final battle, they experimented with Groot’s light spores and how they emanate from his arm to light up the lower levels of the Dark Aster. His abilities culminate in the cocoon he creates around the heroes that he uses to protect and save them from the Dark Aster crash.
 
Throughout, previs helped achieve realistic CG-to-human interactions and CG-to-CG interactions for such sequences. Earl said, “We supplied extensive techvis for every scene we worked on with Rocket and Groot. Starting from the previs for each shot, we would create maps showing where the CG characters were in relation to the practical set and our live-action heroes. Because our 3D sets were precisely built to match the practical sets, we were able to deliver accurate maps.

“Similarly, because the techvis reflected exactly what they were seeing in the previs, James, Steph and the production team could use it as a starting point for blocking scenes with Rocket and Groot. From there, they had the flexibility to either go with what had been developed in the previs or make changes on set.”

Prison Break

While the escape from the Kyln Prison was a major action sequence, it also includes the point at which the Guardians come together as a team for the first time. Therefore, the director wanted to build strong character and humour elements into this sequence. The choreography and visual effects were very complex, but by the time of the shoot, Proof provided James and Stephane with a great deal of data to enable them to work quickly while on set.

The Kyln prison was one of the biggest sets Marvel has constructed for a movie, but still had to be extended from two stories to 30 with a proper extension, fully built, lit and rendered by Framestore. In most circumstances a matte painting would have been a more efficient approach, but this environment would be viewed from so many different angles that a 3D build was essential.

“With Steph, we figured out how many stories would be built for the practical set, and also created a guide for how many floors we would need to see in the shots,” said Earl. “We built both the practical set and the CG extension set into our previs to give the VFX team a clear guide to what James was looking for. Once we handed our assets off to the vendors, they ran with it and made it look amazing.”

3D Integration

The postvis team did lot of work on the interior fight scenes of the Kyln Prison escape. The interior shots needed special attention because, as the battle progresses down various corridors and angled rooms, the actors slam against walls and grab set props. The scale of the interiors had all been worked out during previs, as were the distances travelled by each character and the key walls they would hit.
 
Theresa said, “The live action shoot was on a large but simple green screen set with some of the walls in place. We re-built the 3D model of the set extension to match the lighting and textures from the practical set. Then we added a bit of atmosphere to help convey distance. Each live action shot had to be tracked and have its camera located within our virtual set. We rendered out each shot of the virtual set then composited it with the colour-corrected live action plate mixed in with a bit of atmosphere and interactive lighting. The entire sequence was built, shot by shot, to make sure that the CG extensions worked as planned. This information was shared with the final VFX vendors so they could use it as a starting point for their work.”

The Space Pod sequence is an exhilarating chase scene that follows the lead characters as they escape from the film’s villains. The sequence feels fast, vicious, and dangerous making the audience feels as though these characters could be killed at any moment. James had very specific beats he wanted to hit but gave the Proof team a good deal of freedom to come up with interesting shots and choreography, while maintaining the overall goals of the action he had in mind.

For example, when the character Peter Quill uses the Space Pod to rip open the Necrocraft, Proof’s team devised the idea of putting him into a dive – fitting perfectly with the fact that Quill was falling the entire time and added an extra level of danger to the sequence.

Team Transformation

Once back in at Proof’s studio in Los Angeles, Earl and the previs team transformed into a postvis group. Stephane Ceretti said, “James, Earl, the editors and the VFX department put a lot of effort into completing a version of the director's cut made up entirely of postvised shots. We couldn’t have shown the movie without fully post-visualizing the two CG characters Rocket and Groot, all the spaceships and aerial effects, as well as adding in backgrounds and set extensions for many of the green screen sets. This involved more than 1,900 VFX shots to postvis, which meant we had a huge task ahead of us.”

Earl considers that the postvis requirements for this film were more extensive than on any show he has worked on so far. “We did postvis for pretty much every VFX shot in the film. It was critical for editing. With two CG characters, the editors needed as much material from us as possible to lock down their cuts. Also, the postvis had to be finished to a very high quality to help James through this process,” he said.

“As the edits were being worked on, he needed the best representation we could provide of our hero characters and any set extensions we'd see in the film. That meant the tracking, roto, animation and rendering all had to be rock solid. His goal was to use the postvis as a seamless first pass of what each of the final visual effects shots should be. When he sent scenes off to the vendors, he wanted to give them any notes they might need to get what he was looking for and make the shots work.”

CG Character Postvis

The initial focus of the postvis was on shots that featured the characters Groot and Rocket. “We had Sean Gunn in a green screen suit performing as Rocket and another actor in a green suit with a Groot head on a stick to provide eye lines for the other actors,” said Theresa. “As the plates came in from editorial we immediately tracked them and cleaned them up. Cameras were taken into Maya where our team lit and animated the CG characters over background plates, and rendered out as elements for the compositors. We also added whatever additional props and effects were needed to tell the story.

“For this project, we wanted to take the postvis composites to a higher level than usual so that the work could be used in screenings for the director, editor and other people involved in the development of the sequences. This helped them visualize the final look of the sequences and served as a great jumping off point for the VFX vendors.”

Toolbox

Proof’s team used Maya for all of the previs work, combined with a suite of proprietary tools they have developed to help them to work faster and more efficiently. They also relied on their new real-time CGFX toon shader, and wrote the new CGFX fur shader for Rocket. For the postvis, further to these tools Syntheyes was added for tracking and Nuke for composting.

Theresa said, “In postvis all of the 3D assets, such as set extensions and props, were first modelled, textured and lit in Maya. Then we would decide if the best approach was to render those elements in Maya and save out the frames for compositing, or to export the assets and render everything directly in Nuke. The idea is always to balance speed and quality. We want to work fast, but we also need the shots to look good. Sometimes quick changes to cameras or action are easier in Nuke, in which case there’s no need to go back through Maya first.”  www.proof-inc.com

Words: Adriene Hurst
Images: Courtesy Marvel Entertainment