Cinematographer Wally Pfister with director Christopher Nolan (center) photograph Heath Ledger with the IMAX camera. Photo credit: Stephen Vaughan.

Upgrading on All Fronts
To handle the IMAX format, Double Negative increased its render farm from several hundred to over 2,000 CPUs, and added significant amounts of high speed, high bandwidth storage. It also made key improvements to its pipeline, included comprehensive integration of all assets into an easily accessible published database. The team developed a new lighting toolset that accurately modeled a huge range of real-world lighting fixtures and illumination types. This was then combined with a point cloud illumination baking pipeline, which resulted in detailed lighting setups that could be managed and rendered with great efficiency. Another new important tool was dnSpangle, a lighting preview real time hardware renderer that is tightly integrated with proprietary Rex/PrMan render pipe. Combined with the point cloud illumination tools, this enabled the artists to get results very quickly without having to hit the render farm with requests for preview renders.

"Once we had committed to building this setup, we concluded that it would be just as easy to do all the standard 2.35:1 work on the show at 4K rather than 2K," Franklin observes. "We eventually delivered around 370 finished shots for The Dark Knight, but the data created was sufficient for a show with well over 3,000 shots at standard 2K resolution."

Framestore also treated IMAX resolution as a combination of 5.6 or 8K, depending on the shot. 3D renders and 2D elements were created at one or the other of these resolutions. On the other hand, Buf worked at either 5.6K or at 4K anamorphic: "It is much heavier to handle, but in the end, you really obtain a quality that clearly sets the movie apart from anything that one can see on a DVD at home," Vidal notes.

PacTitle Digital and Cinesite also contributed extensively to the film's visual effects, but were not involved in the IMAX effort.

The Ultimate Challenge
The great paradox of the movie is that most of the visual effects work is seamless, but those shots will be shown in greater detail than any visual effects work in mainstream film history! "I'm very proud of the work that we did," Davis concludes. "A lot of people won't even know what we did. All the houses did a fantastic job, and they really took on the IMAX challenge with great enthusiasm."

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.