'Zodiac': Recreating a Nightmare in CG

If you have the QuickTime plug-in, you can view clips of the vfx work from Zodiac by simply clicking the images.

"Zodiac" was an infamous real life serial killer who committed a series of random and brutal murders in the San Francisco Bay Area during the late '60s and early '70s. Like Jack the Ripper, the killer built his own legend by sending cryptic letters to the newspapers and taunting the police. Although the case remains unsolved, Robert Graysmith, an editorial cartoonist at the San Francisco Chronicle when the murders occurred, investigated the case in a heavily documented book, which has been turned into a chilling thriller by director David Fincher (Se7en). Opening March 2, 2007, from Paramount, Zodiac features extensive, albeit invisible, visual effects work.

Matte World Digital and visual effects supervisor Craig Barron were called in to create more than 40 establishing shots of San Francisco as it looked during that tumultuous era. Several of these shots, including flyovers, required building complete 3D environments. Parallel to this effort, Digital Domain was asked to focus on the exact recreation of the actual murders. The team was led by visual effects supervisor Eric Barba, vfx producer Lisa Beroud, CG supervisor Karl Denham, compositing supervisor Janelle Croshaw and matte painting supervisor Wei Zheng.

"We had to reproduce very precisely the way the killings occurred, and the environments in which they took place," Barba says. "We did more than 100 shots, but most of them will go unnoticed by the viewers. The bulk of our work, in terms of man-hours, involved set extensions. We recreated specific areas in San Francisco as they looked [at that time]. David was very adamant that everything looked exactly as it was at the time the murders occurred. He wanted to shoot his movie as if a camera had really been there. To start with, he decided that, whenever possible, we would shoot the plates at the actual location of each murder. Obviously, the environments had changed quite a bit in the last 35 years, so that's where we came in, to digitally bring them back to their original state."

Camera Projections

One of the most complex sequences was the murder of taxicab driver Paul Stine in the affluent Presidio Heights neighborhood. The plates were shot on a minimally built set of a couple of doors and steps leading to the doors surrounded by bluescreens. The art department drew up architectural drawings of the neighborhood to give the matte painting department a starting point.

"The murder took place at intersection areas of Washington and Cherry streets," Wei Zheng explains. "The sequence involved a couple of dozens shots, which covered 360° of the neighborhood. To achieve realism, we chose an approach of camera projections to create 3D matte painting environments. It involved modeling 3D geometries, painting camera maps using actual photographs of the neighborhood and then projecting maps back to corresponding models. Today's Washington and Cherry neighborhood provided us good references in terms of architectural styles, look, size relationships, etc. Using 3ds Max, we modeled 19 houses matching the real ones, and also built streets, sidewalk of the late '60s and early '70s, cars and a fire truck, power lines, stop signs, trees, etc. The camera projections technique allowed matte painters to utilize his or her painting skills and take advantage of real photo references at the same time. We then used 3ds Max to project the maps onto the geometries."

The maps were created from hundreds of day and nighttime reference photographs, all shot at 4K resolution. "I found out that daytime pictures were more useful," Zheng continues. "With the camera projections technique, you would like to have as many pictures as possible. Typically, you will need front and side views of a house to have a sense of its overall look. A matte painter should be able to paint something with little or nothing to go. Yet, I was hoping we never had such bad luck that we didn't have any pictures to start with. It was the case with one of the hero houses that had two big trees in front of it. We didn't have any ideal photo available. So, a lot of painting work went into that house. Since it was a nighttime scene, there were many streetlights, house lights, doorway lights that we needed to reproduce with their true luminosity. Typical digital images carry a value of 0 to 1, which can't represent the wider luminous value of lights. Unlike most software on the market, Digital Domain's proprietary compositing software, Nuke, truly supports high dynamic 32-bit images that carry a luminous value beyond 0 to 1. Knowing this ability of Nuke, we generated two 16-bit passes: the hero pass, and the core of lights pass. We brought those two passes and other elements into Nuke to re-build our high dynamic pictures. As a result, the images have a much wider range of luminous value. The lights in the scene are brighter and more vivid on the big screen."

The recreation of the environment turned out to be a much more demanding task than what had originally been thought. "A tremendous amount of work went into that sequence," Barba recalls. "For instance, we had police cars in the foreground and bluescreens in the mid ground. It meant that there was no reflection of the background houses on the vehicles. We had to build CG cars specifically to create those reflections, and then put these back in on the real vehicles. Some of the effects that we created were afterthoughts from David. They included adding a CG policeman on a motorcycle and a period fire truck, all in motion. For this type of work, we used either Maya or 3ds Max, depending on which renderer we thought was the most appropriate for any particular element. The vehicles were created in Maya and rendered in V-Ray, our main render engine on this project."

The camera projections technique came in handy when Fincher presented Digital Domain with an unexpected and challenging request. A night sequence involving a murder attempt had been shot on a deserted road besides a parked trailer, but the director was unhappy with the footage. Instead of going back on location for another night shoot, he asked Barba if the scene could be recreated by combining bluescreen footage and CG elements. "We photographed the actors and the trailer separately on bluescreen," Barba explains. "The shot was supposed to be the point of view of the driver of a car that comes upon the scene. So, we shot that element separately too, and later added all the reflections on the windshield. To allow for the proper perspective change, we projected the actors' image onto CG cards. They were then combined with a CG trailer that was built using photographs of the real vehicle projected onto a crude geometry. The entire environment was also created in CG, using the original footage as a reference. Earlier in the sequence, the characters drive by a gas station that was also completely created in CG. Most of the 3D work was carried out in 3ds Max and V-Ray."

Recreating a Murder in CG

As if the environment wasn't demanding enough, the Stine murder itself necessitated months of exacting work. Fincher wanted show it exactly as it happened, down to the minutest details, including the way the bullet entered the cranium and how the head reacted. The director and the visual effects team used police and autopsy reports to recreate the precise chronology of the death. "The Paul Stine murder was a challenging effect for all involved," offers Digital Domain digital artist Marc Perrera. "It was less technology and more artistry. We used our standard tool set that includes Maya, LightWave and 3ds Max, as well as our own proprietary software, such as Nuke and Storm. We first created a 3D geometry that matched the topology of the actor's head, and matchmoved it into the scene using Track, our in-house 3D tracking software. Once we had geometry that matched the movement of the actor, we then had to create believable blood and particulate matter, as well as a gruesome entrance wound that matched the coroner's photographs from the actual case file."

One of the unique aspects of the murders shoot was that Fincher didn't want to use practical effects, such as squibs or fake blood. These techniques didn't allow him to obtain an exact match of the actual event. In order to have total control, the director asked Digital Domain to create the blood and mayhem digitally. Early on, the crew decided that a fluid simulation was the only solution to produce realistic enough results for the blood.

"We created a cavity in the head geometry to act as a vessel for the simulated blood, with a channel leading out to the entrance wound that the blood would flow out of at great speed," Perrera comments. "Deformations, like ripples in the skin from the shock wave of a point blank gun blast, and tearing skin around the entrance wound, were animated in Maya until we had the perfect timing for the motion and timing of the shot. Once that animation was locked, it was on to fluid simulation and, as anyone who has worked with any type of simulation software knows, there is no fast solution. You simply must have an artist sit, adjust numbers, run the simulation and a day later (if you're lucky), see what you get. You repeat this process until you have the look that you are trying to achieve. We were trying to force simulated liquid through a very small channel at a very high speed, which is probably one of the most computationally heavy and tricky things to do. For three months, an artist sat and tweaked the settings in our simulation software until we had the perfect consistency and feel of the blood."

For the lighting, the team took the same approach that Fincher took for the live- action plate. Absolute realism was the goal, which meant that the artists avoided putting the perfect back light to highlight certain areas of the blood, or tweaking the lighting to exploit the effect itself as they would, traditionally. "We used HDRI, image-based lighting, to light the scene," Perrera adds. "We utilized images captured on location and stitched together to create an overall lighting environment that exactly matched the location lighting and, except for some minor tweaking, let the chips fall where they may. This led to a very gritty and shockingly realistic look that gave you the feeling that you were voyeuristically witnessing an actual event. Additionally, supplemental particulate matter and blood spray were created using [3ds Max's] internal particle system. When all was said and done, the original plate was projected back onto the head geometry, shadows were added to the deforming areas of the skin, any interior surface of the wound showing was surfaced with a bloody, wet shader, and the whole thing was then rendered in [3ds Max] using a combination of V-Ray and Max's internal scanline renderer. All these separate elements were then layered together and integrated into the frame using Nuke."

A similar technique was used for the other murders, but due to the way those scenes were shot, the effects were created on a smaller scale. One scene required a specific approach, though, as the victim was stabbed with a knife, and not shot. The sequence was filmed with a knife equipped with a retractable blade and no practical effect on the actress playing the victim. Barba's team tracked a CG blade into the scene, and digitally created the stab wounds. The victim's clothes were animated in 2D using Inferno to simulate the entry point of the blade. The blood was very skillfully painted in 2D onto the character's costume.

"It was a strange movie to work on," Barba concludes. "During our research, we got to look at photographs of the actual crime scenes. These people actually died, and we were retelling the exact way it happened. In many ways, it was sensitive material. Zodiac was not the kind of movie that you celebrate walking around with your typical crew jacket"

Alain Bielik is the founder and editor of renowned effects magazine S.F.X, published in France since 1991. He also contributes to various French publications and occasionally to Cinefex. In 2004, he organized a major special effects exhibition at the Musée International de la Miniature in Lyon, France.