Inception has been short-listed for an Academy Award in the best VFX category, along with five other films that Double Negative worked on in the past year, including Iron Man 2, Scott Pilgrim vs the World, The Sorcerer's Apprentice and Prince of Persia. Sam Dallas recently spoke to the company about its work on Christopher Nolan's latest thriller.

Brainy blockbuster Inception – director Chris Nolan’s follow-up to the hugely successful The Dark Knight – has had people talking around the world.

Talking about the “mind-boggling” plot, the characters, the locations and of course the phenomenal visual effects.

Visual effects supervisor Paul Franklin, of London-based company Double Negative, says the effects were never meant to take over the feature, which took $7.3 million in its opening weekend at the Aussie box office.

“All of the shots do what they're supposed to which is to support and enhance the narrative without ever upstaging the drama,” Franklin tells INSIDEFILM from London.

In total there were 560 VFX shots – of which 500 ended up in the finished movie; in total that amounted to about 30 minutes of screen time (roughly one fifth of the movie).

He says 500 shots for a movie isn’t huge compared to the recent crop of big VFX blockbusters.

“That typifies Chris Nolan's approach to the use of VFX in his films – he uses VFX where it counts,” Franklin says of the London-born, LA-based director.

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The infamous "Paris folding" scene

Franklin’s relationship with Nolan, 40, goes back as far as 2005 hit Batman Begins. He was also the visual effects supervisor on The Dark Knight.

“Chris liked the way that we built our pipeline around the requirements of his films rather than trying to force the work into a pre-built setup and he also rated our creative input into the process,” Franklin says of his company.

“I was blown away by my initial reading of the script – it was immediately obvious to me that this movie was going to be something special, particularly when you took into account the incredible array of talent in all the other departments that Chris had put together.”

Although many of the scenes were dream sequences, they were still shot on location – whether that was LA, Calgary, Tokyo, London or Paris.

Early on in the 148-minute film, Cobb (Leonardo DiCaprio) takes Ariadne (Ellen Page) to a dreamworld version of Paris. The location was a small bakery which was turned into a small sidewalk café.

After Ariadne, a brilliant architecture student, discovers she’s actually dreaming, a series of explosions occur near the café before she ultimately wakes up.

For the in-camera explosions created by English special effects supervisor Chris Corbould (Casino Royale), air mortars were used to blast lightweight debris.

High-speed film and digital cameras captured the blasts of anything up to 1000 frames per second (more than 40 times the normal speed of 24 frames per second).

This had the effect of making the “turbulent” debris look like it was suspended in zero gravity.

“Double Negative re-timed the high-speed material to create the impression of explosions that slow down – as if underwater – and then used proprietary dynamics tools along with Houdini to add secondary layers of shattering debris,” says Franklin who worked on the film from March 2009 till May this year.

“The end result is a sequence in which the collapsing dream rapidly falls apart, spinning away into violent chaos.”

Certainly one of the biggest and highly spectacular visual effects scenes in the $US160 million film is the “Paris folding scene”.

After Double Negative studied the Paris location, Lidar Services (Watchmen) scanned buildings for them before the London-based company created a series of Parisian apartment blocks.

Franklin says CG supervisor Philippe Leprince (Superman Returns) implemented the new ptex texture mapping techniques in Pixar’s RenderMan to allow the team to avoid the “laborious” UV coordinate mapping that is usually associated with models of this type.

“The final folded streets featured fully-animated cars and people – anything that's not on the flat in the final images is CG,” he says.

Mal and Dom's dream world

Theatre goers will remember the scene early on when Ariadne creates a bridge out of the echoing reflections between two massive mirrors.

“During pre-production we worked up various concept animations of the bridge assembling itself in a blur of stop-frame construction, but it always ended up looking slightly twee and overly-magical,” Franklin explains.

“Chris was interested in something elegant that, whilst simple in concept, would defy easy analysis by the viewer.

“In an early discussion I mentioned that from certain angles the arches resembled the infinite reflections generated by two opposed mirrors.

“Chris thought that this was an interesting idea and eventually asked the question: ‘what could you do on set with a really big mirror?’”

A massive 8×16 foot mirror was built making sure it could swing shut on a hinge.

“This gave a great start for us in VFX, but as big as the mirrored door was – its size being limited mainly by weight as it was already up to 800 pounds – we still needed to do a lot of work,” Franklin says.

The support rig and crew reflections were then removed and then endless secondary reflections from the environment were added in.

“The result is a series of shots so subtle in their execution that you're not really aware of any digital intervention until the very last moments of the sequence,” Franklin says.

“In fact most of what you're looking at is digital with only the actors being real – even their reflections are digital doubles in many cases.”

Later in the film, Yusuf (Dileep Rao) speeds through the busy streets of the rainwashed city. At the end of the scene, he reverses off an elevated bridge and we watch it as it plunges in super slow-motion towards the river below.

Throughout this sequence, Franklin explains, the visual effects team had several tasks to complete.

The first came in the moments when the van’s timeframe slows down considerably.

“The original material had been shot at 24 fps [frames per second],” Franklin explains.

“Double Negative had to slow it down to an effective 720 fps.

“The initial speed change was made in Double Negative’s proprietary 64-bit compositing system but even the most sophisticated optical-flow-based retiming produced unacceptable image artifacts.

“In fact the source material – a heavily motion-blurred van in a downpour – was about as bad as it gets for this kind of approach.”

Franklin says his company, which had about 220 staff working on the film at various points, had to pretty much rebuild the entire shot to create the effect of time slowing down.

“The van's geometry was recreated with animated planes inside Shake and layers of slow-motion rain and road surface spatters were painstakingly added as CG animation.”

For the shots of the van plunging off the bridge, Corbould rigged a full-size van to be blasted off the raised mid-section of the Commodore Schuyler F. Heim Bridge in Long Beach, California.

“The huge size of the bridge meant it was impossible to rig the shots for practical rain so we opted to shoot the material clean and add rain in post as layers of VFX animation,” Franklin says.

“CG girder and debris elements were added to increase the perceived impact of the van as it soars out into space and worked hard to eliminate retiming artifacts caused by slowing the frame rates even further from the initial 720 fps.

“The shots of the dreamers going into freefall were created with a van interior set mounted on an SFX gimbal rig.”

During this scene, Arthur (Joseph-Gordon Levitt) was thrown into a weightlessness environment and was obviously on wire rigs on both vertical and horizontal sets – Franklin’s company was responsible to remove the wires and rigs.

Later in the movie we discover Cobb and Ariadne washed up on the shores of Limbo.

Ariadne looks in wonder at the crumbling towers of the city that Cobb built with Mal (Marion Cotillard), whilst they were trapped in the depths of the dream.

Wading out of the surf, Cobb and Ariadne advance into the derelict streets and head towards the centre of Limbo where they see the gallery of Cobb's dead dreams.

The scenes of Cobb and Ariadne in the surf were shot on a beach in Morocco.

“A large trailer clad in green screen panels was placed in the sea to provide interaction with the waves,” Franklin says.

“The greenscreen box was then replaced with crumbling CG buildings and the shoreline was built up with the procedurally generated glacier cliff face of Limbo City.”

The architecture of the city was based on reference material of early modernist buildings including Constructivist (Russian revolutionary) and Bauhaus (1920s German) structures.

This article originally appeared in the September issue (#135) of INSIDEFILM magazine. Inception is now out on DVD.

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