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Step by Step: Greece: Secrets of the Past

Apr 1, 2006 12:05 PM, By Ellen Wolff

Secrets Revealed in IMAX

MacGillivray Freeman Films of Laguna Beach, Calif., is acclaimed for making large-format adventures like Everest, but its latest film took the company into new terrain. According to director/producer Greg MacGillivray, Greece: Secrets of the Past contains the most labor-intensive single IMAX theater sequence ever done — almost four minutes long.

It begins at dawn, as a helicopter flies around the ruins of the Parthenon, one of the seven wonders of the ancient world. That shot then dissolves to a wire-frame “fly around” of what the original architecture might have looked like (a visualization technique that archeologists use in their restoration efforts). As the wire-frame depiction ends, the sequence segues into a ground-based dolly shot that reveals a group of archeologists outside of the building's present-day ruins. The camera pushes past them, and the live-action dolly shot blends into a CG transformation of the Parthenon. The famed columns are digitally restored, brightly colored friezes appear, and huge bronze doors swing open. Light floods into the interior and reveals a 40ft. gold statue of the goddess Athena towering above a reflecting pool. The camera moves around Athena and looks back at the open doors — just as the archeologists walk into a room not seen in 2,500 years.

“It's all designed as one continuous shot,” says Craig Barron, visual effects supervisor at Matte World Digital in Novato, Calif.

Barron's team was brought onto the project by the film's CG consultant Paul Debevec of USC. (MacGillivray had seen a CG short created by Debevec in which he'd used Lidar scans to digitally recreate the Parthenon.) “Paul graciously shared his data with us,” notes Barron. “Our challenge was to take his assets up to IMAX resolution, which required more details and new textures.”

Barron himself visited the Parthenon to do additional surveying with laser rangefinders. “It was important to measure things like the depth of the reflecting pool so that we could restore it properly in CG.” He explains, “We didn't use Paul's Lidar data directly. We used his model of the Parthenon ruins and his reflective texture data for how the marble should look in a computer-rendered environment. His work was our foundation.”

Matte World's post process began with the stabilization of the IMAX plate photography (done with Andersson Technologies SynthEyes software.) The modeling team then set about recreating the building and the long-lost Athena statue in CG, using a combination of Autodesk 3ds Max, Debevec's data, and their own measurements. But their first step was low-tech — a foam-core box containing columns and a cutout doorway. Barron says, “We took this box outside to see what happened when sunlight came through the door and bounced off surfaces. Before we get into CG, we often do ‘reality checks’ on what would happen in the real world.”

The most challenging task involved rendering all the elements at IMAX resolution. Barron says, “Every frame is eight times a normal movie frame. We absolutely pushed the envelope on rendering.” Matte World used SplutterFish's Brazil renderer, which had a good raytracer and could handle huge file sizes. Matte World had just invested in a phalanx of new Windows-based PCs. But Barron says, “The render machines couldn't load all the information in their onboard RAM. We had to simplify things in pre-renders.”

Barron stresses that what makes the Parthenon interior look convincing is the realistic lighting. “The interior has radiosity rendering and indirect illumination from the doorway. The pool also reflects the room's interior,” he says. Meanwhile, the bright gold Athena statue was rendered separately, so that her reflective surface could be controlled in compositing, independently of the background.

The rendering was complicated by the need to add lens distortion, notes Barron. “One of the major issues of making this CG look like it belonged in an IMAX film was to mimic the linear lens distortion of the wide-angle IMAX lens,” he says. “We asked Greg MacGillivray if he could really shoot a restored Parthenon, what lens would he use? Then we took that lens and photographed grids that had been pre-measured, so that we could find a transform for the distortion of the lens. We essentially mapped the lens onto the inside of a sphere so that we could copy it and apply that distortion to our renders. Brazil was able to create that lens distortion. Of course, our renders had to be even bigger so that they could have that distortion.”

“It took a while to feel OK about this process,” Barron admits. “On a computer monitor it looked distorted, but then we'd project it on a curved screen and it looked correct.” To check out their shots before committing to full renders, Barron's team would render selected frames and then project those frames in Sony's San Francisco IMAX theater.

The final element — the live-action shot of the archeologists standing in the Parthenon doorway — was shot at Matte World. “We had established our lighting direction for the interior so it was just a matter of making everything line up properly as we shot them,” Barron says. “We shot on 35mm film because this element was going to be reduced in the IMAX frame.” Compositing was then done with Apple Shake, and 2D texture corrections were handled with Adobe Photoshop. According to Barron, “[The final CG] in some ways is similar to our cardboard cutout.”

Despite all the detail work and the challenges of rendering 5,520 IMAX frames, Barron says, “Creating a classical building that you can walk through was a dream job. Until this project, most of my knowledge of Greek mythology had come from Ray Harryhausen movies.”

CREDIT ROLL

Director	-	Greg MacGillivray
Director of Photography	-	Brad Ohlund
Helicopter DP	-	Ron Goodman, SpaceCam Systems
Parthenon 3D Imaging	-	Paul Debevec
Visual Effects Supervisor	-	Matthew Muller
For Matte World Digital:
Visual Effects Supervisor	-	Craig Barron
Executive Producer	-	Krystyna Demkowicz
Producer	-	Kip Larsen
Editor	-	Ken Rogerson
Art Director	-	Chris Evans
CG Artists	-	Glenn Cotter, Morgan
Compositing	-	Paul Rivera, Todd R. Smith
Athena Sculptor	-	Sean Joyce
Rotoscoping Lead	-	Daphne Ackerson
Digital Technicians	-	Can Chang, Jaymie Lam
System Development	-	Simon Walton

© 2008 Penton Media, Inc.