CGSociety :: Production Focus
23 September 2010, by Renee Dunlop
The day has not yet ended on the Twilight films, and in the latest, Twilight: Eclipse, we are treated to another taste. As before, Tippett Studio handled much of the wolf work, and this time Image Engine was on board for the vampire crystallization and flashback sequence.
It was not an easy assignment; constrained by a relatively low budget, around $65 million for the entire film, the two studios had to be creative on what they could provide.
Image: Tippett Studio
Image Engine worked on over 300 shots with vampire deaths, loads of compositing work and set extensions, a flashback and a ravine sequence with digital wolves, totaling more than 20 minutes of screen time. Image Engine has always been an R&D focused company so for roughly four years they have been working on an open source toolkit called 'cortex'. As explained by R&D Developer Tom Cowland, "it was an open source project started by the studio as a way to save everyone having to redo the same work all the time."
How does this apply to Eclipse? Because when Image Engine needed a fur system set up in order to handle the complexities of the wolves, they took a look at off-the-shelf solutions but in the end decided in order to get the rapid turnaround they needed, it was best to design the solution themselves based on their cortex system. They developed it modularly, dynamics, shading, grooming, and of course the backend of the system. In this way, they designed a system of various bits that could be expanded or refined as needed.
By expanding on the Marschner paper to achieve the desired specular and diffused lighting, occlusion, and lighting from the environment, "we work on specific tools for specific projects. That helps up to produce technology which works it's way back down into the open-source toolkit. Consequently, anything in that toolkit has been rigorously tested." The outcome was a fur system that was quite proficient with short hair- but then along came the digi-double of Victoria with her long flowing bright red curls in the scenes with Victoria running from the wolves, the shots had to be convincing at two-thirds frame height, with the head at about an eight of a frame.
While flexible, 'cortex' is not a node-based system where blocks of software can be added and subtracted at will. It is slightly more structured, keeping things simpler for the artists. In 'cortex', for example, the base of the hair is generated, then gets passed through a series of modifiers. "It allows us to add new sections while the artists can still have a fairly coordinated interface and don't have to wade through a big graph to find things," explained Cowland.
"Stephenie's writing in the novel is fairly explicit in the way the vampires kill each other," said Visual Effects Executive Producer, Shawn Walsh.
"There is a certain level of beautiful horror about the way vampires die."
The shatter effect deals with the Twilight lore in that vampires can't be killed because they are a crystalline form of their former human self. The only way they can be killed is by another vampire or by the jaws of the wolves.
A meeting with director David Slade provided the vampire limitations that Slade and book author Stephenie Meyer wanted.
Some of the limitations were:
1) Slade didn't want the vampires to sparkle similar to diamonds, he preferred hot points of white light.
2) Meyer stated they needed to break into pieces about the size of a fist, no smaller, and they needed to be rigid when they broke. And
3) since this was a PG rated film, the vampire deaths couldn't be too gory.
Nigel Denton-Howes, CG Supervisor, Assets, was tasked with finding an appropriate solution. One material hits all those points, namely crystal. Crystal will focus light into hot points, grows naturally into fist sized pieces, and it's rigid. "Crystal also has the additional benefit of lots of different varieties so we can get something that looks a little bit like muscle structure or a little like fat, or like skin.
I got some cross sections of people from the Visible Human Project and we did a bunch of computer paintings replacing the muscle with one kind of crystal that grows in a shard or block, the skin would be like a polished fogged glass."
Just as in any normal day in the life of an artist, Denton-Howes proceeded to photo some of his colleagues and digitally lop off their heads, filling in areas normally reserved for the human inner workings with painted visualizations of how a vampire might appear when they are breaking apart.
The concept art, all based on actual crystals found in nature, showed the muscles as larger blocks with striations, the fatty tissue was a little softer so would break and was a separate lay created from a fine-grained foggy glass type of crystal that almost looks like jelly in the light, and the skin was smooth and polished with crystals so small it appeared almost like human flesh.
The surface is where the smallest crystals are but the deeper into the body you go, the larger the crystals get.
The muscles ended up being quite transparent. "We were focusing on seeing the background through there, but the light would be refracted, bent as it went through it, but you could still see what was going on behind the actor." The fatty tissue was less transparent. But the bar was raised when it was time for the shots, "when we actually had to determine on a piece by piece basis how it was going to break apart." Depicting a violent scene under PG rules, while remaining true to Meyer's storyline and the directors vision involved a balancing act.
Even 'simple' set extensions were monumental tasks. The scene where Bella, Edward, and Jacob are camping out on the snowy mountain-top required a major set extension. The scene was partially filmed in August on Mount Seymour near Vancouver, when there was no snow, and partially filmed in a film studio that was filled with fake snow.
That required merging roughly 140 shots, replacing the mountain summer environment with a snowy winter one. That sequence alone involved roughly half the work on the film. Image Engine handled snow background plates and snow falling, while Tippett Studio handled the snow clumping to the wolves.
Tippett Studio was asked to return on this film after their work on New Moon. Working with a team of about 60 people, they created new wolves according to Spades' preferences. "We had a mandate from David [Slade] to make the wolves as photorealistic as possible," says Eric Leven, VFX Supervisor at Tippett Studio. "He wasn't a fan of the way they looked in the second movie, where we made them look a certain way because that is what Chris Weitz wanted."
And in a first for this series, added a great deal of interaction between wolves with humans and vampires- and snow that had to match the fake snow used on set. "We shipped a 55 gallon drum of fake snow back from the set because they had a very specific mixture of snow," Leven continues. "It was half shredded paper and half some sort of polymer," provided by a company in London.
The digital snow was a particle based system that would generate to stick to the hairs that had their own effects animation. Aesthetic decisions such as how far into the hair, how big, the color. The snow particles were paint map driven, both in initial placement and in falling off. "We would kill particles in the fur, and create new particles in the exact same position that would follow a different set of physical guidelines." The snow shaders were relatively simple, not requiring any sparkle.
The battle sequence between the newborns and the six foot wolves weighing 1000 pounds was another sequence of great strength. The actors playing the newborns were shot in close proximity to each other, making it difficult to animate the wolves between them as they bit and tore their way through the newborn crowd, a task that had to be handled by Tippett compositor Satish Ratakonda. "We had to come up with something that cheated the distance between the vampires," said Ratakonda.
"Taking more time for the wolves to cross from one vampire to another, and manipulate the contact timing when the wolf is hitting the ground and the vampires." Layering, as the wolves passed in front or in back of the actors, also increased timing. This doesn't mean they spread the actors location over a wider space, it means they created the illusion of space as the wolves charged forward from vampire to vampire. All of this resulted in a great deal of painting was required since the actors playing the newborns were being pulled and jerked on wires and falling on foam mats.
To increase the feeling of the wolves massive weight, Ratakonda displaced the ground around their feet and they came crashing down, and layered in flying grass and debris.
He also used shadows to help create distance between vampires and wolves, adding denser shadows as the two were in closer proximity and lighter shadows as the wolves bounced away to their next victim.
The shadows were created by matchmoving models of the wolves and vampires from the plate.
Ratakonda also kept his eye on the detail. When one newbie was attacked by a wolf who grabbed his shirt, pulling and shredding it, Ratakonda requested a shirt with wrinkles and tears from the paint department.
By animating that single image over a period of frames, he was able to create the illusion that the digital wolf was grabbing a live action shirt, pulling it away until it tore, and the shirt snapping back into position in tatters.