'The Dark Knight': Grounding Batman -- Part 1

The Dark Knight (now playing from Warner Bros.), not surprisingly, sets itself apart from the average vfx-based summer blockbuster. With around 700 vfx shots, director Christopher Nolan's purpose once again was not to wow viewers, but to serve a story in which Batman confronts two of his arch enemies, the Joker and Harvey Two-Face.

Working with Visual Effects Producer Joyce Cox and VFX Supervisor Nick Davis oversaw a global effort that involved vendors based in America, England and France. "Chris Nolan had had a very positive experience with the work that had been achieved on the first movie [Batman Begins], and he wanted to maintain the same gritty, super realistic approach to the visual effects," Davis explains. "He wanted a movie to be as 'un-effectsy' as possible. The shots had to feel real. To this purpose, we did a lot of location work, whereas on the first movie, the majority of the scenes had been captured on stage. The fact that we shot on location, notably in Chicago and Hong Kong, allowed us to ground the movie in reality. We shot as many real elements as possible.

"There is a scene in which Bruce Wayne (Christian Bale) throws a party in his penthouse. Instead of building a set, production decided to use the spectacular lobby of a real office building. It meant that we had to replace everything outside the windows with the scenery that one would expect outside a penthouse. So, we put greenscreens on every window of this lobby and basically used the location as a soundstage, which was quite difficult. But in the end, what we got on screen was this massive space that had a gritty and very realistic feel to it."

Back in Gotham City

Just like on Batman Begins, Gotham City environments and most of the action sequences were assigned to London-based Double Negative. The company ended up creating more than half of the vfx shots, including 170 shots rendered and composited in full IMAX resolution for the special IMAX release of the movie.

In-house Visual Effects Supervisor Paul Franklin led a team that included Senior VFX Producer Matthew Plummer, 2D Supervisor Andy Lockley and co-CG Supervisors Peter Bebb, David Vickery and Philippe Leprince. Rather than have an overall animation supervisor, Franklin opted to work directly with the animation team to develop the stunt and vehicle sequences.

Double Negative used its usual Maya/RenderMan/Shake pipeline, associated with a series of new proprietary tools. "For The Dark Knight, we developed several major new toolsets, the most significant of which was our IMAX rendering and compositing pipeline, which is essentially resolution independent -- the only real limitation was how much server space we could cram into the machine rooms," notes Franklin. "The key components to this new pipeline are a suite of 64-bit compositing tools and a highly optimized 3D asset management strategy linked to a super-efficient lighting and rendering pipe."

To everyone's satisfaction, many of the Gotham City geometries that had been built for Batman Begins could be reused for The Dark Knight. One exception was the art deco Wayne Tower, which was completely redesigned for the new movie. "Most of what you see in the finished film is actual Chicago," Franklin adds. "We used visual effects sparingly to extend and enhance the location material only when needed, such as when Chris Nolan wanted to sell the scale of Gotham or when it just wasn't possible to get a plate of a location from the angle needed."

All of the CG assets were completely overhauled, remodeled to higher tolerances and then retextured to hold up to the greater scrutiny of IMAX -- and also to the fact that the new movie featured a lot more daylight photography. The only item that was reused without any modification was the Gotham City Monorail System, as it only played in two shots in the far background.

Rebuilding Gotham

The team found out that a whole new library of photographic material was required to cover the new locations that The Dark Knight used in the city. "For Batman Begins, we had mounted an extensive stills documentation of the Chicago locations – shooting almost one million digital exposures -- but the demands of IMAX and the varied lighting conditions of The Dark Knight lead us to beef up the stills library to get the results we wanted," Franklin observes. "Fortunately, digital stills technology had moved on, and the Canon 1DS MkII digital SLRs enabled us to shoot much faster and at much higher resolution than when we were working on Batman Begins. This lead to a change in our texture gathering strategy: rather than shoot the real buildings under beauty-lit conditions and then re-project the images directly onto digital geometry, we were able to wait until the buildings were completely flat lit in the shadows -- we have a piece of software called dnSun which allows us to predict exactly where the shadows will be in a city at any time/date. We then shot the textures in that brief window of opportunity before the light changed. This would then serve as a base level texture which could be re-lit digitally to match any lighting setup whether it was day, magic hour or night."

Geometry was captured in a number of ways. The team worked with Lidar VFX Services to digitize key locations, and also mounted their own surveys of all locations. The data was then used to reconstruct architecture directly from the texture reference stills via photogrammetry. All the data was collated by the modeling team, which then constructed the digital models, textured them and did the initial base-level look development.

Double Negative created a library of 40 hero buildings that were able to sustain close-up scrutiny. Each building was developed to work in day, magic hour and three different nighttime setups. "In addition to this, we had a huge library of low-resolution background buildings covering most of downtown Chicago," Franklin continues. "We also built detailed models of specific locations, including the Lower Wacker underground roadway, LaSalle Street (the site of the Batpod chase/truck flip scene). These models included accurate models of the actual road surfaces, which turned out to be essential later on during the car chase sequence. All items were built to work in hero close-ups with very high-resolution textures, and the shader set was able to efficiently manage the resolution requirements. The aim was to be able to reproduce as a minimum requirement the same degree of flexibility with our scenes that a cinematographer would expect to have on a real location. Our dnAsset digital asset management system has a good system for handling multiple levels of detail, which can either be automatically or manually selected."

A New Environment

In the movie, Gotham City is portrayed as a super Manhattan island, completely surrounded by broad rivers and the open ocean. In Batman Begins, Nolan had started to reveal this maritime environment with brief shots of the Gotham River and a small number of scenes set in the Gotham dockyards, all sequences created by Double Negative. In The Dark Knight, the viewer will go right out on the water, looking back at the city while a hijacked passenger ferries float helplessly, completely at the mercy of the Joker.

To create the water surfaces, the team rewrote their dnOcean toolset, which uses Fourier Transforms to simulate a variety of wave types. A powerful water surface shader set then completed the effect. "We optimized dnOcean for speed, and also added new feature to create the wind patterns that you often see affecting large bodies of open water," Franklin explains. "Whenever you see the ferries, they are 100% digital, except for moments when they are seen in close-up at the dockside with the actors: a small section of the stern was built as a physical set for that. All of the water in the ferry shots is always completely digital, as it was easier to replace everything in the shot rather than try and blend the digital water with the real water in the plate."

The ferries themselves were based on the Staten Island ferries that shuttle between Manhattan and Staten Island in New York City. The team traveled to New York along with a crew from Lidar VFX services, and documented the actual ferries. A highly detailed digital model was built from the data and textured to work in close up at IMAX resolution, though in the final event, all the shots were delivered in standard 2.35:1 format. Passengers for the ferries were created by shooting extras as greenscreen elements that were then placed on cards and tracked into the shots with Double Negative's dnPlane-it 3D compositing toolset.

From Batmobile to Batpod

Besides creating Gotham City, Double Negative was also in charge of all the key visual effects involving the Batmobile and Batpod. The company had already created a digital Batmobile for Batman Begins, but the vehicle only appeared in long shots. "Initially, we had expected to be doing more of the same for The Dark Knight as the actual physical Batmobiles created by Chris Corbould's special effects team are capable of just about any kind of stunt," Franklin suggests. "So, we restored our digital Batmobile model to the system, and began to clean it up for background duties. However, it soon became apparent that the only application for the CG vehicle would be during the scene where the Batpod emerges from the car's wrecked shell.

"This would require our Batmobile to pass muster in extreme close-up at full IMAX quality. Furthermore, this necessitated replicating the look of the wrecked car rather than the clean version seen in Batman Begins -- the match needed to be perfect as we cut from a live action shot of the real Batmobile to a digital version within the same shot. The team worked very hard to get the level of detail up to scratch, and we liked to joke that our digital version was more detailed than the real thing as we added a whole bunch of interior details (revealed as the Batmobile transforms itself into the Batpod) that didn't exist in the real car…"

The concept for the release of the Batpod required very intricate mechanical articulation of the car's structure combined with wild over-revving and slewing wheel spin, which wasn't possible to set up as a practical effect under the restrictions of the shoot schedule. The Batpod is finally revealed as the Batmobile's exterior armored panels explode off in a shower of fragments. The slewing wheel spin was animated via keyframe, while the panel wobble was driven by Double Negative's in-house rigid body solver dnDynamite. The dynamics toolset was also used to blow the panels off the car and send them skittering around the underground freeway.

The Batpod's key feature is the pair of oversized tires that come from the front end of the Batmobile. "We developed a special animation rig that allowed us to slide the wheels out from the exploding wreck of the Batmobile whilst smoothly animating the Batpod on its crazy ride down the street," Franklin adds. "The digital Batpod was built from a detailed Lidar scan of the actual practical stunt bike, and textured to play full screen at full IMAX resolution. We also built a special Batman stunt double for the sequence in order to match the look of the stuntman who was riding the bike during the chase shots."

Creating BatdoublesM

Cyberscans of both Christian Bale and stunt driver Jean-Pierre Goy -- both in the Batsuit -- formed the basis of the digital double models. Unlike in Batman Begins, the new Batsuit features a complex exoskeleton of sliding armor that required a separate animation rig running on top of the character rig. No motion capture was used -- the animation was completely keyframed.

The Batcape was the one part of the costume that didn't change between the films, which allowed the team to reuse some of the geometry from Batman Begins. "However, the demands of IMAX meant our cloth simulation needed to be much more detailed," Franklin observes. "The final cloth animation is a combination of the Syflex cloth simulation plug-in for Maya, Maya's own N-Cloth simulator, soft body animation and had keyframed shape animation. For the Batpod chase sequence, we had to heavily modify our cloth simulation techniques in order to match the vigorous flapping and whipping of the real thing. The Batsuit's unique texture was created via a custom set of shaders that generated a lot of the surface detail procedurally, with additional hand-painted maps controlling specularity."

Double Negative met another match-the-real-thing challenge with a helicopter crash sequence. The digital crash had to bridge the gap between shots of the live action chopper flying down LaSalle Street and a practical in-camera special effects burning helicopter wreck tumbling along the road deck. "Working from Lidar scans and photo reference, we modeled a high detail IMAX-ready Jet Ranger chopper which was animated via key frame to catch the cables laid in its path by the Joker's henchmen," Franklin notes. "The high angle shots of the chopper also featured completely digital street environments, as it was impossible to get plates of the real street from these positions. For the shot of the chopper crashing into the building, we used a new in-house tool to create the clouds of shattering glass and debris. The final impact on the road featured extensive use of Maya's fluid dynamics and dnDynamite. The explosion is completely digital with no live-action elements used -- the fireball was rendered with DNB, our proprietary volumetric renderer."

Take It to the Next Level

For the team at Double Negative, The Dark Knight presented a welcome opportunity to revisit the world of Gotham City that it had helped to bring to the screen for Batman Begins -- and even top it, as the 2005 movie was already considered to be a high point in the company's history. Then, it had to take it to the next level with the IMAX sequences. "The 64-bit compositing pipeline and the revamped 3D tool set performed way beyond expectation with the result that the terrors once held by 4K and up are no longer of any real concern," Franklin concludes. "The critical response to the movie in early previews has been stunning, and the fact that the vast majority of the critics are seemingly unaware of the substantial contribution that the visual effects made to the finished film only goes to vindicate the monumental effort that everyone on the team put into the show. We hope that The Dark Knight represents a major new stage in the development of digital visual effects as part of the cinematic story telling process. If the audiences believe our artifice to be the real thing, then that's OK by us!"

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, both print and online, and occasionally to Cinefex. In 2004, he organized a major special effects exhibition at the Musée International de la Miniature in Lyon, France.