ILM distilled 'Pirates' water

Developed new tools for film's VFX

As most moviegoers now know, "Pirates of the Caribbean: At World's End" contains a climactic 20-minute sea battle in a massive maelstrom. There is said to be more visual effects in this one sequence than are found in many VFX-driven feature films in their entirety.

The big challenge in this "Pirates" sequence — and the new film — was the water.

Although the industry has seen computer-generated water before, the sequence brought new hurdles to visual effects supervisor John Knoll and the VFX team.

"We had a lot of very difficult shots that featured the water," Knoll said. "The maelstrom was about a mile and a half across, and in order to get enough detail, the fluid simulation has to be at very high resolution. That is a very difficult thing to do because of the shape of the water surface … in all three dimensions."

As a result, the team at Industrial Light + Magic — which was the lead VFX house on the film and which completed about one-third of the film's estimated 2,000 VFX shots — developed new tools to warp and composite the fluid simulation in the sequence. Image warping is a technique used to distort an image and was used to help optimize the resolution. Compositing is the process of combining images to create a new image and was used to composite multiple fluid simulations into a single shot.

Additionally, to complete the sequence, the team had to consider forces like gravity as well as the speed of the water's movement, which had to pick up as the ships moved down the funnel.

Other techniques used by ILM had the advantage of having been developed and put through the paces during production of previous "Pirates" films. Notable was the technique used to create the realistic performance of the CG Davy Jones and crew in 2006's "Dead Man's Chest." This ILM process, called iMoCap, allowed the effects team to shoot and reproduce the actors' performances — used as the basis for the CG characters — on set during the actual shoot rather than separately on a motion-capture stage. The technique was the most trumpeted development from "Dead Man's Chest" and carried Knoll and his team to the 2007 Academy Awards, where they won Oscars for the film's visual effects.

While the same technique was used to create Jones and crew in the third film, Knoll said there was a distinct difference. "In ('Dead Man's Chest'), just getting Davy Jones to work was one of the biggest challenges," he said. "It wasn't until the final month that it was starting to work smoothly. On most shows, then it's over and you don't reap the benefits. In ('At World's End'), there was about same amount of Davy Jones and crew, but now (the technique) was fairly well worked out. That was a very smooth and straightforward process."

As is often the case, new techniques developed for the "Pirates" films are now a part of the ILM workflow and will be tapped as needed for future productions. This includes the new water techniques and iMoCap.

ILM recently was named the lead VFX house on Marvel Studios' "Iron Man." Knoll expects that iMoCap will be used to capture the performance that would be used for the CG versions of Iron Man, to be played by Robert Downey Jr.

"It's a good fit," Knoll said. "(Iron Man) is a human figure, and we want the actor to develop the performance. … It' s an actor- and director-friendly motion-capture (technique)."

Knoll was the VFX supervisor on all three "Pirates" films. As the third opened, he reflected, "They were a great deal of fun. I really enjoyed working on these pictures. Gore (Verbinski) was really a great director to work with."

Knoll is reading scripts and has not confirmed his next project. He added that he "would love to" work with Verbinski again. "I think we work well together," he said.