Cloud-Creation, Miniatures and More
This was Vaughn’s first film in which visual effects played a large role. “He’d talk about the effects using simple descriptions of the movement and ideas he wanted to portray,” Chiang says. “Then, we’d give him key areas where he’d need to make important decisions. And, because he wasn’t influenced by technology, there’s a simplicity to the effects. I think that Matthew’s concept of what he wanted to see grounded the effects. Also, I tried to mix the mediums by using physical effects and miniatures.”
During pre-production, a team of three animators from Double Negative moved into Pinewood studios to previs the visual effects shots and complicated camera moves. “We needed to spend our money wisely,” Chiang says. “We knew we couldn’t compete with the Narnias and the Harry Potters, which have bigger budgets and more resources. But one area Matthew wouldn’t compromise on was the terrain. He wanted the terrain we moved over to be quite sophisticated.”
Thus, while animators worked at Pinewood on previs, an R&D team at Double Negative began sorting out the technology they’d need to create clouds and the land beneath.
First, they looked at what they had built for Flyboys. With Chiang as VFX supervisor, Double Negative had developed two proprietary tools to create the aerial battle shots for the 2006 film: dnClouds and, for the landscape generation, Tecto.
“For Flyboys, we could set up everything in a small environment,” says technical supervisor Gavin Graham. “But, in Stardust, we fly over vast areas of landscape, so we needed more clouds, yet with minimum overhead. We needed a library of clouds.”
Rather than provide a library of canned clouds in predetermined shapes, Graham and his team created cloud “chunks” that artists could piece together to make roiling clouds, billowing clouds, towering clouds, wisps of fast moving fluff and everything between.
The team created these chunks using 3D models and fluid simulations. “Two of the modelers preferred creating the clouds in the same way they’d create a creature or hard object,” says Graham. “They modeled the basics and then took the geometry into ZBrush to make it more cloudy and bubbly.”
Artists creating a cloudy sky could page through thumbnail renders of these models and pull low-res chunks into Maya as building blocks. Once built, the clouds shapes moved into dnB, the studio’s proprietary volume renderer, which filled the shapes with density calculated on a voxel-by-voxel basis. “At render time, we could further tweak the look to make a cloud more billowy or sparse in certain areas,” Graham says.
Similarly, the artists could pick from a library of simulated clouds. “These clouds were geared more toward stormy sequences with roiling clouds that would grow and evolve,” he says. “Also, when the camera was moving slowly and we wanted to see clouds moving in the foreground, we used the fluid sims.”
For example, when Tristan and Yvaine stand on a cloud, they’re standing on fluid simulations from the cloud library mixed with particle simulations. “The particles gave us interactive control,” says Graham. “We could blow them from left to right.”
Beneath the clouds, Double Negative also created digital landscapes. Some shots demanded particular terrains; for others, though, the crew stitched together a scouting location.
“It’s funny,” says Graham. “When people think of CG, they think of the magic effects. They don’t realize that huge amounts of the landscapes are artificial.”
Simply put, the team created the landscapes by draping a 3D mesh with texture maps, rather like covering a lumpy mattress with a sheet. An ordinance survey of Scotland’s Isle of Skye provided terrain data for the 3D mesh, which looked like a big grid inside Maya. Photographs shot from a helicopter and stitched together provided the texture maps. Tecto managed the geometric data and the high-resolution images.
“Because each photograph, that is, each tile, was 4K resolution, we needed to limit how many appeared in a scene at one time,” says Graham. “With Tecto, we could pick an area, preview it in Maya, and then for each frame, Tecto would load only the areas relevant to the camera into the renderer.”
Double Negative also created 2.5D and 3D matte paintings for establishing shots, set extensions, and backgrounds. “Sometimes we’d fly over miles of landscape up into the sky, down through a roof, and transition into a 3D model and then move into something shot on set,” says Graham. “Sometimes, we’d transition into a painted projection.” For compositing, the studio uses Shake; for rendering, RenderMan.
Establishing shots of the witches’ lair, for example, which is inside a sinkhole, use a combination of 3D models and matte paintings. “The characters go from one to the other,” says Graham. A fully 3D castle appears in a coronation scene and also in establishing shots.
The most dramatic set extension was of the sky vessel. The actors worked on an 80-foot deck built on set; Double Negative extended it to 140 feet and lifted it into the air.
To track the camera for these effects shots, Chiang used a Leica total-station surveying tool. “It fires a point out and measures it in space,” says Chiang. “If you needed to do a box, you could zap all eight corners and know exactly where it was relative to camera. We’d do it at the start and end of the camera positions, and the middle, if needed. We’d get a series of dots floating in the air in 3D and as long as we knew where the zeroes were, we could relate it to the set. We’d also take photos from the same position.”
For a ship sequence, for example, they used several points on the deck as the “zeroes.” “Whenever we needed a camera position, we zapped those points first so we knew the relation of the camera to the set,” Chiang says.
The crew took sample HDRI lighting and high-resolution digital photographs on set, as well. “We had a few all-CG shots with the sky, landscape, ship, and digital doubles,” says Graham, “but the majority were green-screen shots of the actors on deck.”
One of the all-digital shots showed the ship crash-landing into a lake ‘ well, it was mostly digital. “Water is one of those CG animals that’s constantly being tested by film,” Chiang says. “It’s a hard effect to achieve, so because of that, I decided to shot a lot physically.” Chiang shot the water around the Isle of Skye from a helicopter, and also shot a power boat rippling the water of a reservoir. “That way we didn’t have to get into particle and fluid dynamics,” he says.
When the airship crashes into the practical water, though, the crew at Double Negative replaced the water surface with 3D to generate holdouts and mattes for the three shots that needed 2D ripples added to the water.
Although the large, invisible environments comprised much of Double Negative’s work, the studio also worked on one of the most obvious magical effects in the film: Lamia’s green fire.
“At first, we had a huge, complicated, over-the-top green flame coming out of Michelle Pfeiffer’s finger,” says Chiang. “Matthew made us temper it back to a simpler idea, almost like a Zippo lighter.” But sometimes, when she points, the flame grows higher.
To art-direct the witch’s fire, Graham’s team decided to give animators small particle simulations. “The animators would send maybe 100 particles along a curve so they could direct them any way they wanted them to move,” he says.
The effects team then moved the approved particle simulations into a system that converted them into geometry, generating springs, soft bodies, and joints for ribbons of fire that seemed magical and alive. “Imagine a single particle traveling along,” says Graham, “streaming a soft body behind like a sheet flapping in the wind. The geometry had cloth-like behavior but it is a soft body driven by a network of bones with springs attached to them, almost like a snake wiggling its tail like a sine wave. Over that, the soft body reacts to forces.” Parameters controlled stiffness, velocity, when the soft body releases, and other attributes.
For a grittier witchy effect, that of a bird changing to a woman and back again through thick black smoke, the crew art-directed the transition with paintings. “We had 20 frames in which to do the transition, to drive the fluid simulation,” says Graham. “The painted velocity grid told the fluid in what direction to travel in a section of 3D space. We stored it as a velocity field, and that pushed the fluid simulation around.” Feeding the colors of the dress into the fluid simulation helped complete the illusion.
In addition to effects created at Double Negative, Lip Synch created light effects around Claire Danes, transformed Michelle Pfeiffer from an 80-year-old witch into a young witch, and extended the witches’ lair.
Senate sent lightning bolts out of a box in the final battle, created a witch’s red flames, and extended the wall between the real and fantasy worlds. Baseblack removed rigs in a fight sequence, built and animated a CG push-me, pull-me elephant. Machine helped a character drown in the air and handled bluescreen comps. Rushes did set extensions and explosions. And, Cinesite created the ghostly effects.
“I was running all around London with Matthew approving shots,” says Chiang. “Because the technology is so much more accessible now, small companies can do individual pieces of 3D. It’s neat to give them a chance to explore more complicated work rather than having them only doing the simplest stuff.”
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