Timing was everything when it came to creating the effects for Road to Perdition, a feature film set in Depression-era Chicago. The story line focuses on a hit man whose wife and youngest son are killed when his private and personal lives collide, and details his subsequent journey of revenge, which he takes with his surviving son in tow. In the live-action drama from DreamWorks/Fox, set designers re-created this stormy time period in the Windy City's past. However, for one particular sequence, Cinesite, an effects studio based in Los Angeles, transported viewers using digital imagery that was precisely tracked and integrated into the scenes.
 |
| Cinesite projected images of Chicago's past on the car windows for this dramatic live-action scene in Road to Perdition, a period film. To mask the fact that the entire sequence was shot at a different location, paper was placed on the windows, blocki |
The 45-second segment opens as the camera focuses on the hit man, played by Tom Hanks, who is seen through the windshield of his car as it approaches the city. His son, who had been sleeping in the back seat, awakes in amazement as he sees the impressive cityscape for the first time, with reflections of tall buildings playing on the windows. As the car drives away, the shot pulls back to an overhead view showing the car passing over Chicago's LaSalle Street Bridge.
To create the splendor of the sequence, Cinesite lead compositor Ted Andre seamlessly combined imagery from two separately filmed locations in Chicago to simulate the 1931 period look. The live action for the entire sequence was filmed without greenscreen at the LaSalle Street set location. For the first portion of the shot, the car was stationary, though it was rocked gently to help simulate actual forward movement. Certain windows on the car were covered with opaque white paper, which was digitally replaced with moving background footage that was filmed at the Belbow Street location and then composited into the live-action scene using Kodak's Cineon software running on SGI's Irix platform. When the shot progressed to the appropriate point, some of the paper was removed from the windows to reveal certain LaSalle Street backgrounds.
Visual effects supervisor Michael McAlister set up three cameras on a truck, in a panoramic fashion, with overlap between three different images, to capture the background footage that would later be used to create the illusion of movement in the car element. According to Andre, the background plates were anamorphic, or squeezed cinemascope, that had to be stitched together to form one continuous plate. As a result, even the smallest amount of jitter would be amplified because of the additional distortion that cinemascope lenses inherently introduce at the edges where the plates meet. To overcome this situation, Andre removed the distortion, and masked the "stitched" seams using parts of the car.
"At the edge of the frame, these plates had a tendency to slide against each other if the stabilization was the least bit off," Andre says. "So it was imperative for this step to be done with extreme accuracy, to prevent issues with the positioning of the horizon line." He used Cinesite's proprietary tracking software for most of the background stabilization, with some of the elements requiring more than 800 tracking points due to the nature of the camera move. Once the plates were stabilized, digital camera shake was added to simulate motion, making it appear as though the car were moving along the road the entire time.
Using a combination of Cineon and proprietary software, Andre gathered motion data from the foreground car element and applied it to the background images (at a percentage, to account for parallax) so that when they were composited, the two perspectives would match. "For the overall positioning of the horizon line, I ended up having to do a lot of hand tracking. Procedural methods work up to a point, but then it becomes an artistic call," explains Andre.
Because the car windows did not contain glass, reflections had to be digitally inserted by compositing the background buildings at a low fade value, which was then animated at a higher or lower value when necessary. The low fade value facilitated the illusion of semi-transparent reflections. "The director, Sam Mendes, wanted the reflections to convey a sense of wonder as Michael Sullivan Jr. [the son] awakens in the back of the car," says Andre.
 |
| Cinesite artists gave this cityscape scene a digital makeover by removing modern streetlights and replacing them with period elements, and erasing all other traces of the present day. |
For the latter part of the shot, when the car travels over the bridge, an extensive digital makeover was performed on the original raw footage. "Because it's such a wide shot, each item had to be addressed individually in terms of motion and perspective. It was extremely detailed, painstaking work," notes Andre.
For instance, Andre painted out construction fences on both the left and right sides of the frame; removed all modern signage, road lines, and various markings; replaced the double yellow line with a single white line; removed two large streetlights in the foreground of the shot and replaced them with period lights; and "Greeked out" (made unrecognizable) modern concrete details. Moreover, he replaced all 16 lamps that run down the center of the bridge, removed or replaced buildings to reflect the period, and even changed the colors of certain buildings. Some of the buildings needed to have their windows cut in half as well, since the earlier buildings had smaller windows.
Andre used Cineon for the painting, matte work, tracking, and final compositing of the various items in the makeover section. One of the biggest challenges, he adds, was addressing the myriad details in achieving this period makeover. "Since there was a lot of very fine detail, I had to do much of the work at full 2K base resolution (2048 by 1556 pixels) locally, rather than using subsampled versions" he adds. "For certain things that required articulate rotoscoping, I enlisted the help of Cinesite's roto department, which used proprietary software."
The finishing touches on the makeover included the addition of the "el" train, CG birds, and "God," or light, rays. The train was a practical element filmed at the same location, while the CG birds were created in Alias|Wavefront's Maya, and the God rays were done in Adobe Systems' Photoshop.
For tracking and replacing many of the items in the makeover, the group used a relatively new technique, originally devised by Andre and Cinesite's 3D manager Jeff Baksinski for work done on the film Rat Race. "We used [Science-D-Vision's] 3D-Equalizer to create a 3D camera track of the entire shot, which was then exported into Maya," explains Cinesite motion tracker Dante Quintana. "We could then render out a black-and-white image of the specific points that Andre needed for the comp." These elements consisted of white spheres moving on a black background. "I would then import these into Cineon, and selectively track the spheres that corresponded with specific objects," Andre explains.
During the makeover, the tallest streetlights closest to the camera posed the highest degree of difficulty, as they had to be replaced with completely different and much shorter lamps. Replacing them, says Andre, also meant replacing the tops of the foreground towers and the larger building surfaces that were overlapped by the more modern, extended lamp heads. This procedure was accomplished by tracking the lamps in Cineon, and then replacing the towers with virtual set elements created in Maya.
"For the LaSalle Street shot, I had to use every 2D technique that I knew, and create a few new ones along the way." says Andre."
The final sequence, which is approximately 1100 frames in length, plays as if it were one long take, filmed at one location. "It doesn't look like an effects shot at all; rather, a grand reveal of old Chicago," adds McAlister. "In the context of the film, the sequence appears untouched."..
Karen Moltenbrey is a senior editor for Computer Graphics World.
TOOLSAlias|Wavefront www.aliaswavefront.com
Kodak www.kodak.com
Science-D-Vision www.sci-d-vis.com
SGI www.sgi.com