Cinefex Weekly Update | Issue 23

The production staged the conflict in a valley in County Wicklow -- ironically, near the Irish town of Hollywood. "We called the valley the 'Hollywood Bowl,'" Johnson said. "Physical effects dressed the area with fake snow to create the impression of a snowy, icy bank, and snowed up greenery on either side of the location as high as the snow-spraying trucks could reach. Visual effects then created the world beyond that, enhancing what was there and, in some places, replacing a lot of what was shot on location."

To assist environment extensions, Johnson's team positioned portable greenscreens behind actors wherever possible on location, but mostly relied on postproduction means to add digital enhancements - surveying the location, then motion tracking and rotoscoping performers from backgrounds. "We didn't want to place restrictions on Antoine and his director of photography, Slawomir Idziak," said Johnson. "There was a limited amount of time to shoot the scene, so they kept camerawork very fluid with a lot of Steadicam and camera movement. We filmed half the scene in Ireland, concentrating on Arthur and the knights, and some of wider establishing shots of the Saxons. We later shot Saxons against bluescreen on the backlot at Pinewood Studios in England and created the environment behind them. Antoine decided to replace the real environment behind the knights, as well, so the scope of the effects expanded during postproduction."

To create digital frozen lake environments, Cinesite layered digital matte paintings into 3D settings using '3D Space' -- a plug-in for Shake, developed by digital artist Michele Sciolette. "We took a 3D track from our production plates and created 3D camera moves in Maya," Johnson explained. "We took that data into 3D Space and then added layers of matte paintings, which ranged from 3K to 8K resolutions. We assigned sections of each painting to correctly proportioned 3D markers within Shake and created a sense of parallax and perspective shift from the 3D camera."

Compositors created crowds of Saxon warriors using digital replication. For selected shots, the team made use of artificial intelligence crowd simulation technology, developed in-house as 'React,' applying motion capture of battle reenactment and stunt performers to 3D animated warriors. "The AI assigned different parameters to different marching and fighting movements," said Johnson, "and then React integrated that within Maya and RenderMan. We used React to generate 3D characters in our final climactic battle and during the ice battle, where we're underwater looking up through the ice. Everything in those shots -- from the particles floating in the water, the ice, feet hitting the ice, bodies fading off -- was completely computer generated."

CG ice required a complex volumetric shader, seen close up when Arthur's knight, Dagonet (Ray Stevenson), swings an axe to shatter the frozen lake beneath the Saxon army's feet. Neil Corbould's physical effects team built a mechanical rig for the shattering effect on Pinewood Studios' backlot paddock tank using giant gimbaled sections of ice, engineered to tip stunt performers. Cinesite digitally replaced the ground beneath the performers' feet with computer generated ice using custom shaders to create depth and refraction in all frozen surfaces.

The ice shader used ray tracing to create light refraction and scattering effects. Compositors layered elements using environment maps, occlusion, shadowing and particle elements and mixed in live splash and snow elements as bodies fell into the lake. Cracking effects were entirely computer generated, with animated displacements and procedurally driven fragmentation effects filled with volumetric elements that simulated the internal structure of the ice - bubbles, ice shards, and tiny 3D frozen leaves adding to the detail.

"We created a lot of subtle elements to give the shots a real-world feel," commented Johnson. "It was a fantastic story, but it was grounded in reality."