Most of the vfx work for RockNRolla was done with Shake, with some Maya and Renderman. A greenscreen shot of Thandie Newton smoking out of the car window looks like it was shot for real. All images © Warner Bros. Courtesy of Rushes.

London, as seen in Guy Ritchie's most recent film, RockNRolla (expanding today from Warner Bros.), is a fast-paced, funny and at times dangerous place, full of quirky criminals whose philosophy can easily be summed up as "shoot fast and get out clean."

The same is true of the making of a Ritchie movie, and RockNRolla is no exception. The movie stars Gerard Butler, Tom Wilkinson and Thandie Newton in a tale of con men and gunmen that moves quickly though the streets of modern, boomtown London. Shot in a six-week period on location, the film required a similar approach to visual effects shots that needed to be invisible rather than spectacular.

Keeping the work on the film local, Ritchie turned to London-based Rushes, tapping the company's head of film and TV, Jonathan Privett, to supervise the work.

"Our sister company, Ascent 142, were already in conversation about the digital intermediate for the film, and were called to see if anyone could provide advice for a vfx shot, ironically filming within walking distance," says Privett. "As one of Rushes vfx supervisors and head of film and TV, I walked over to the location and got involved."

In keeping with Ritchie's style, Privett says the visual effects were meant to be as minimal and invisible as possible. "As much as possible was done in camera," he says. "As a director, Guy was very much focused on the performances and feel of the film."

Most of the challenges were logistical rather than technical. "Due to the commitments of the actors a large amount of in-car green screen shots were required because no time was available to do a low-loader shoot," adds Privett.

Such shots may seem simple, but present more than their fair share of challenges. "I have always thought that these seemingly simple shots are difficult to make truly convincing in a studio environment," continues Privett.

To get that level of realism, the cars were mounted on turntables to get some motion into the foreground of the shots. They also took extra time to allow director of photography David Higgs to light the greenscreen shots.

Rushes made a car explode from footage of a vehicle sitting inside a deserted warehouse. A base 3D model of the vehicle was brought into play for the debris and blast reaction. 3D smoke completed the shot.

"The background plates, both day and night, were then shot from a stabilized mount on a low-loader using QuickTimes from editorial as reference for every shot," Privett explains. "The sequences were then roughly assembled in editorial, allowing us to weed out the backgrounds that didn't work brilliantly and replace them with alternate sections. A great deal of care was then taken over the final comps to ensure the result looks great and you are not distracted from the action."

The greenscreen shoot was made easier by the Arri D-20 cameras used to shoot the film. "[It] gave a really nice result for the greenscreen keying due to its low noise," Privett offers.

Privett says most of the work was done in Maya and RenderMan for the limited 3D work, with Shake being the predominant tool for compositing. In all, Rushes had a crew of between four and eight artists working 10 weeks to create 173 shots for the film.

The technique resulted in Privett's favorite moment in the film: A greenscreen shot of Newton smoking out of the car window. "It really looks like it was shot for real," he says.

Despite shooting on the real streets of London, there were still occasions where Privett's crew had to create shots to match Ritchie's vision. One such scene called for a shot of a large yacht in the Docklands area of London that had to be created from scratch as the crew had neither the opportunity to shoot a plate at the location nor access to a yacht.