Coming off the monster success of Monster House, director Gil Kenan chose the sandbox at Tom Hanks' Playtone Productions and Walden Media for his next project: an adaptation of Jeanne DuPrau's wildly popular novel, City of Ember, about the race to save a dying, underground city well past its 200-year shelf-life starring Bill Murray and Tim Robbins, it opened October 10th.

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It took dedicated farms weeks to render the underground City of Ember, shown here in progressive stages. Clip courtesy of Walden Media and Luma Pictures. (Click to play or right-click here to download mov.)
Close Move

Says Kenan:

The City of Ember is a character in the movie, so it was vital that production designer Martin Laing and I build something as realistic as possible, and the effects team be able to render it. We put ourselves in the position of The Builders, the founding fathers, who hastily built this City to protect their citizens from an unexplained harm, and guessed at what they might need to remain sheltered there for at least two centuries. When our story starts, the City has long passed its 'expiration date.'

Pandemonium of Titanic Proportions

It was originally scheduled as a "fairly humble, establishing shot," recalls VFX Supervisor Eric Durst, of the first time viewers see the generator, a massive—and massively deteriorating—structure located far beneath the City's buildings and streets that illuminates a canopy of lights above, without which the citizens of Ember would be plunged into a void of total darkness and certain death.

Eric Durst
City of Ember's VFX Supervisor, Eric Durst

If the generator is the heart of the City, it's supposed to look as if it's about to go into full-scale arrest, with frantic workers on scaffolding 30 stories high and scores of fire fighters battling electrical charges and smoke, while rivers of water, which power the generator, rush below.

"We were on a huge soundstage in Belfast, Northern Ireland," Durst recounts, "the old Harland and Wolff shipyard where they built the Titanic (no, not Cameron's, the real thing!): 100 feet high, 500 feet long, and 400 hundred feet wide, the only place big enough to build and house our sets.  Once there, we all realized—Gil Kenan, the producers, and I—that since this was such a pivotal sequence, it would require a much more dramatic approach on a grander scale, with more actors, elements, and sweeping camera movement than originally planned."

In that moment on set—and they happen often on large-scale, effects-driven films like City of Ember—the creative team had to think fast (every idle hour burns up thousands of dollars in production costs) in order to ensure they captured enough "coverage," that is, native, in-camera footage with live actors on the set, plus pick up shots of various "elements," like workers on scaffolding, in order to have all the data needed to enhance the scene and match everything digitally in post-production.

(One element the filmmakers couldn't capture was explosives. With a history of bombings from "the troubles" in Northern Ireland, film permits for anything with pyrotechnics are nearly impossible to obtain. So, the sparks and fire, which look incredibly photo-real, are actually computer-generated.)

Durst describes a sweeping shot for this first glimpse of the generator (dubbed "the pandemonium scene"), a combination of in-camera crane and Steadi-cam footage, plus CG, later "composited," (digitally "blended") in post production by VFX house, Luma Pictures. "The camera swoops over the shoulder of 'Doon' (Harry Treadaway) one of the lead characters, and booms up to reveal this generator of titanic proportion, then does a 180-degree reversal to track Doon as he backs away from the chaos."

Doon sees the city
Young Doon sees the massive—and massively deteriorating—generator that powers the underground City for the first time in a complex, composited shot; image courtesy of Walden Media and Luma Pictures.

Says Vince Cirelli, VFX Supervisor for Luma: "This shot had everything in it! An actual set, a CG set, live actors, plus 3D CG objects such as the generator, water and fire. And the whole sequence had to be timed to a CG camera move." Luma worked closely with Production Designer Martin Laing, whose team built out the first floor of what was to be a thirty-story space, in order to ensure the virtual set matched the actual set. "We're very proud of the seamless result we were able to achieve," says Cirelli. "Seamless" is Durst's watchword for effects that are, well, effective.

"Visual effects should support storytelling, not vice versa," says Durst, who has spent nearly thirty years in the VFX industry, starting out in hand-drawn animation at Cal Arts—whose alumni include John Lasseter—before working on one of his first feature projects, TRON, which he calls "the world's greatest hand-drawn, 'computer-animated' film." Later, Durst joined VFX pioneer John Dykstra at Apogee, the precursor to ILM, where he directed commercials—he's the mind behind the memorable animated Volkswagon campaign, "Fahrvergnügen,"—then went on to effects supervision for other features such as End of Days, The One, Batman and Robin, and Spiderman 2. (You can view some of Eric's work, including a racy, banned-in-the-U.S.A. George Michael video, "Freeek!" in the YouTube gallery we created here.)

Back to the Beginning

While the "pandemonium scene" was changed on-set, on the fly, the opening credit sequence was modified after principal photography had wrapped and the initial effects were completed. As Durst tells it, the original opening sequence began tight on what is revealed to be a filament in a light bulb. Then, the camera pulls back and that light bulb becomes one in a sea of bulbs lighting up the entire City of Ember. "We fly over the City," says Durst, "and tilt down to reveal 'Lina' (Saoirse Ronan) as she descends a flight of stairs. The camera tracks her to ground level and follows her as she runs through the streets and into the town square." Sounds good, right? And it was, an impressive continuous shot combining live action and CG created by French effects house, Buf.

Virtual city of Ember
The virtual City of Ember set had to match the actual set built on a shipyard-cum-soundstage in Northern Ireland where the Titanic was built (no, not Cameron's…the real thing!) Image courtesy of Walden Media and Luma Pictures

But when Director Gil Kenan began editing the film, he felt that the introduction of Lina was premature, and that a scene between Doon and his father, 'Loris' (Tim Robbins), discussing the dying city was needed to introduce the story. The new scene would have been simple enough to shoot—if all the sets had not been struck (torn down) months earlier. So, Durst brought in Amalgamated Pixels (Get Smart, Nim's Island) to help solve the problem. "Our solution was not to re-shoot the entire opening sequence," says Amalgamated's Executive Producer, Michael Morreale, "but to insert a newly-shot exchange between Doon and Loris into what Buf had already created."

The challenges were manifold: create a camera move that would match the move created by Buf months earlier; build a virtual replica of the actual set and all its real-world "dressing," including pipes, surface texture, wires and signage; drop the actors (who filmed their new scene against a green screen) into the "Doon's apartment" set seamlessly, and do it all without getting "busted," Morreale's term for those moments when obvious computer effects or imagery distract from the story by pulling the viewer "out of the moment."

First, the team at Amalgamated used software such as Maya to "rough out" the set—the building that housed Doon's apartment. "We didn't 'dress it' or apply any texture at this juncture, just got the shape and dimensions right," says Morreale. Then, using pre-visualization software, they were able to take Buf's computer-generated camera move and "do the math" to figure out exactly how the camera needed to move—crane position, speed, etc.—when the actors shot their new scene against a green screen on a sound stage. Once Kenan approved the "pre-viz," the actors were assembled, the scene was shot, and Amalgamated began combining, or compositing, the live action footage of the actors with the newly-created CG set, and integrating this scene into the entire opening sequence.

Amalgamated worked on another important sequence, this one involving clouds and light. "It was shot with the actors against green screen and background plates, beautiful matte paintings," recalls Morreale. "But it was too static. The clouds needed to be animated, and the light and shadow on the actors' faces had to change accordingly." The team set about making the clouds more "volumetric and dimensional," a process that Morreale says involved as much artistry as technology in order to make everything look natural. "But, as the great Disney animators always said," he notes, "nothing in nature is ever 'natural.'"

Water, Water…Everywhere!

Luma Pictures' VFX Supervisor, Vince Cirelli, would wholeheartedly agree. His company was tasked by Durst with creating not only a "natural-looking" giant, star-nosed mole that chases Doon and Lina through the City of Ember, but also the realistic-looking river and the generator powered by it.

CG Water
When a CG object like flowing water hits an obstruction, like a river bank, it breaks into thousands of pieces, making the image exponentially more complex to render. Image courtesy of Walden Media and Luma Pictures.

"They should add 'water' to the list of things that are difficult to work with in film, like animals and children," laughs Durst, who says the filmmakers originally considered using millions of gallons of actual H2O before deciding that working with real water was prohibitive. "But CG water is notoriously complex to render," says Durst. There are many different kinds of water—clear, muddy, gently flowing, cascading—and, because of its reflective and transparent properties, its look is influenced by its environment and all available light sources, both natural and artificial. Making matters more difficult, when a CG object like flowing water hits an obstruction, like a river bank, it breaks into thousands of pieces, making the image exponentially more complex to render. Now each one of these thousands of objects must reflect and refract light, whereas, originally, there was just one.

"We believe effects development is one part hardware and software, and three parts ingenuity," says Cirelli, whose company's strategy was to deliver as many iterations, often low-res simulations, of the "rushing river" effect as possible to Durst and Kenan for their feedback, before rendering the high-resolution versions, which would take weeks to render on a dedicated render farm.

One of the most difficult water "set pieces" was a scene in which Doon and Lina are chased on a boat speeding through a labyrinth of underground rivers and rapids. Using fluid-simulating software RealFlow, the Luma team started by submitting low-resolution "roughs" for Durst and Kenan's approval. "At this early stage, the water looks like gelatinous goo," Cirelli explains. "The main purpose of these low-res simulations is for the director to get a sense of the speed, shape, and density of the water."

Luma programmers then wrote scripts (in C++) to partition the simulation into much smaller portions, chunks of the cave, so to speak, that greatly sped up the revision process. When all of the smaller, diced-up sections of the simulation were complete, Luma simulated them together so that the various elements would properly react to each other. As Cirelli notes: "When running simulations based on real-world physics, it can be difficult to trigger specific events throughout a timeline. We took an inverted approach to our simulations and 'sculpted' the way the water thrashed down the cave by modifying the virtual cave floor."

To make the rushing water slow down, for instance, a series of horizontal divots, channels and ramps were created on the virtual cave floor to make it "lap up and roll on itself during a tight turn." Initially, Kenan wanted the river rushing at a speed of approximately 70 mph, but "in the real world, water would explode up the sides of the cave wall, as if blasting from a hose," says Cirelli, "so we amplified the property of gravity by six times in order to 'choreograph' the rushing water to Gil's specifications."

The Biggest Star in the Picture

Kenan had very interesting specifications for the giant, 6-foot star-nosed mole that chases Doon and Lina through a maze. "If you've ever seen a real star-nosed mole, it's quite a creepy creature," says Cirelli, "with these tentacles that extend from its snout." What the director wanted is for the mole's nose "to react first, then its body to follow." As it got closer to Doon and Lina, for instance, the mole's nose would start "twitching with rage, or, in its more inquisitive moments, would feel around and explore with its tentacles."

Star-nosed mole
The real star-nosed mole is one of nature's creepiest creatures...
Star-nosed mole
...but the virtual star-nosed mole is no pageant winner either. Image courtesy of Walden Media and Luma Pictures.

Of course, the team responsible for creating the star-nosed mole studied the real thing. In fact, says Cirelli, "Our head modeler was lucky enough to find an actual star-nosed mole on his property in Pennsylvania." The biggest challenge in creating a furry CG creature like the star-nosed mole is getting its skin and fur to "roll up and bunch and jiggle," as it would in real life.

"We made two extreme, but very rudimentary, versions of what would become the mole in Maya," says Cirelli, "one with very soft, pliant properties, almost like a pillow, and one that was more rigid. We painted the areas we wanted to 'bunch up,' and in a very short time, we were able to sculpt realistic muscles and skin." Another challenge: "scaling up" the mole. As Cirelli explains, "You'd think a large, fat, furry creature would sort of lumber along, like a bear, but Gil wanted the CG giant star-nosed mole to be fast and quick enough to give the kids a run for their money which, of course, ratcheted up the drama during the chase."

"We're excited for audiences to get out and see the film," says Durst. "Hopefully, if we on the effects team have done our jobs right, they won't even notice us."