World War Z is a different kind of zombie movie. While the classics of the genre from Night of the Living Dead to 28 Days Later are micro-to-low budget films with intense violence and gore (at least for the time), World War Z is a summer blockbuster with a 15/PG-13 rating that’s pitched at a wider audience – and on an epic scale.

The film has come in for some criticism for its lack of in-your-face entrails eating – as well as using a different storyline from the multiple separate episodes offered by the Max Brooks book it’s based on. But according to London-based Cinesite's VFX supervisor on World War Z, Matt Johnson, the creators of the film didn’t just want to just make a zombie film without the graphic violence to sell it to a bigger audience. The aim was to use the bigger budget afforded to a $100-million-plus Hollywood movie to show zombies overrunning the planet in a way smaller films could not, and to redesign the concept of the zombie to work in a more open-world and with a full-spec VFX budget – creating a type of ghoul you’ve never seen before.

(Well, this is what at least some the creators wanted, apparently. The convoluted – and expensive process – of World War Z’s birthing with rewrites, reshoots and a six-month delay in the film’s release is well documented. It also saw two overall VFX supervisors, with John Nelson replaced by ILM's Scott Farrar along the way. However, being from Digital Arts and not Variety, I eschewed digging for film-industry gossip in favour of discussing Cinesite’s creative process with Matt.)

“The movie clearly has a vast scale,” he says. “It’s a tentpole summer blockbuster and all that goes along with that. What we did as part of the design process is work out how the aesthetics of the zombie could be made to work with a broader canvas.”

That canvas is a globe-hopping journey of Brad Pitt’s Gerry Lane from his initial encounter with the zombie outbreak in Philadelphia (though filmed in Glasgow). It moves to the apparently safe, walled city of Jerusalem (actually Malta), and then to an ocean-going floatilla of boats. While the zombies themselves start from the usual template of a relentless creature who attacks on sight and whose bite will infect the recipient and turn them into a zombie, they’re unlike the slow, lumbering shufflers of Night of the Living Dead.

Compositing a mass zombie attack: (from top) footage shot in Glasgow, CG zombies, the initial low-res composite, and the final shot.

World War Z is probably the first to feature scenes with tens of thousands of zombies (crowd controlled through Massive). Zombies traditional sense of menace comes from their slow but unstopaable stagger – but at cityscape level, this could have easily ended up being rather dull.

“Many of best zombie movies have used a confined environment to their advantage: [for example, in Dawn of the Dead, the protagonists are] trapped in a shopping mall and you've got zombies endlessly smashing against the windows,” says Matt. “That works fantastically well when you have a contained [environment for your] story. If you have a whole square of people and you have 50,000 people running across it [pursued by zombies], it's not going to play so well. You can't have running people and slow-moving zombies in the same frame – it doesn't work aesthetically [for any sense of threat or danger].”

Fast-running zombies aren’t a new concept – 28 Days Later springs immediately to mind – but the filmmakers wanted to use the time, budget and VFX expertise they have access to make them move in a completely inhuman way. Even in Danny Boyle’s masterpiece, the zombies instinctually act like humans because they are – they’re actors in (rather convincing) make-up who lunge, fall and perform other forms of movement constrained by unconscious behavioural limits (such as not wanting to hurt themselves). For World War Z, the filmmakers wanted their zombies to have no such inhibitions – slamming their bodies around with no sense of personal safety.

To get the type of motion he wanted, Matt first worked with experimental dancers, ballerinas and movement artists – including one of the lead puppeteers from the stage version of War Horse.

“These people spend their lives doing the most astonishing things with their bodies,” says Matt. “They brought the aesthetics of contemporary and experimental dance and ballet – and all of that rigid technical training that goes along with that – to being able to express through their physically what happens when you're bitten and the virus (or whatever it is) is taking over your body.”

Cinesite motion-captured performances from the dancers to create models of how the zombies should move, as well as capturing a lot of video reference. However, brilliant those they dancers were, they could only take the team so far.

“It is human nature, if you're running and diving to attack somebody, you will always put your arms out first. It's just preservation of yourself as you do it. With a zombie, there is no self, no feeling or fear of damaging yourself."

Matt Johnson

“We looked at references beyond what even the finest stunt people could do. We looked at animals, and what we settled on were these Israeli attack dogs and Alsatians that are trained to leap and get the bite in: fearless and teeth-first. This is what we had to do in CG – as it's genuinely not physically possible – and it’s used throughout the movie.”

This proved quite the technical challenge for Cinesite’s team, as this meant that full-CG zombies would be in the foreground of shots attempting to bite and knock-down real actors – with a seamless final composite that fits with the film’s ‘not shouting about its VFX’ aesthetic.

Matt describes the World War Z’s overall visual feel as “early-to-mid-70s” and “almost pseudo-documentary”, referencing films such as The Parallax View and All The Presidents Men.

In keeping with that aesthetic, much of the raw footage was shot with rear-netted lenses – where material from a nylon stocking is put over the back of the lens to soften the look of the film, and add bloom to the highlights.

“Being somewhat geeky, I got them to remove the back-netting from the lenses during the greenscreen shots – as I didn't want it to bugger up the edges [between the real and CG elements],” explains Matt. “But it was very important that we put that look back so it would sit and fit with the rest of the movie.

This was achieved using tools and scripts Cinesite created for The Foundry's Nuke compositing application that automatically applied the rear-netted effect to the final composite.