The SFX of Gravity: achieving the impossible
This is an old feature that has been republished for TechRadar’s Movie Week. The original piece was published on March 03, 2014.
It is hard for a blockbuster nowadays to deliver the all-important ‘wow’ factor. Audiences in the 21st century have been conditioned to expect expensive special effects – so much so that they are only usually noticed now if they fall short of being exceptional.
When it comes to Gravity, though, it was not the audience’s expectations that had to be met but that of the director’s.
And with good reason: at the Oscars this week, Gravity won seven Academy awards – including Best Director, Best Visual Effects and Best Sound Editing. But Alfonzo Cuaron’s view of space isn’t just multi award-winning but groundbreaking too.
Cuaron is a director that has been obsessed with space for most of his life, so when it came to delivering his ‘space’ movie it had to be unlike anything that had come before it.
The effects Cuaron wanted to achieve simply didn’t exist so he needed to consult a team of effects artists to achieve the impossible and bring his unique Oscar-winning version of space to screens.
This is where Framestore came in. Famed for bringing the likes of Iron Man, RoboCop and Dr Who to life, the London-based company was chosen to work on Gravity because of its prior involvement on Cuaron’s previous movie Children Of Men.
But as TechRadar found out when it recently spoke to Alexis Wajsbrot, CG effects supervisor on Gravity, even though they had worked with Cuaron in the past, nothing quite prepared them for what they had to achieve next.
Creating the unknown
"Gravity was different from any other project because we started very early on when there was just a script," said Wajsbrot.
"Alfonzo went to Framestore and spoke to Tim Webber who was the effects chief on Children Of Men and asked: ‘how do we do the effects?’"
The answer was… well, for a long time there wasn’t one. The effects Cuaron wanted to achieve had never been done before, so everything had to be built from the ground up. One of the reasons for this was Cuaron’s insistence on long takes – something him and his director of photography Emmanuel Lubezki (affectionally known as Chivo) were famed for.
"Zero gravity has already been done in Apollo 13, where they used what is called the ‘vomit comet’ – a plane that reaches zero gravity for one minute. Tim and Alfonzo did try this but you can only do one-minute takes and only from a certain angle so it wasn’t going to work for Gravity," explained Wajsbrot.
"We had to investigate other ideas, like using cables and different techniques. What we found out was that all of the traditional techniques that had been used in the previous movies wouldn’t work for Gravity because of Alfonso’s directing style. That’s when we knew we had to find another workflow."
This ‘workflow’ came in the form of the previz that was made for the movie. Where the pre-visualisation of a film – a rough animation – is pretty much done for all movies now, Gravity had to rely heavily on what the visual effects were going to look like.
The previz of Gravity was unheralded. It consisted of the whole movie being animated by Webber and the team. Everything apart from the actors was created inside a computer and this was then used by Chivo to recreate with Sandra Bullock and the rest of the cast.
"Chivo said very early on that he wanted the faces to be shot for real, as he didn’t trust CG to do a good enough job with faces. This was going to be very complex but if the movie was full CG then it would have just been an animated movie," said Wajsbrot.
"Gravity is different. It is an animation movie for 95% of the time but the faces had to be real."
This did pose a problem, however. Lubezki’s cinematography relied heavily on light from the sun, as well as long takes of the characters spinning out of control through space. The CG lighting and the lighting of the faces had to somehow match up seamlessly in these shots.
A solution was finally found which involved keeping the actors static in the shot and using robot-controlled cameras to make it look like the world was spinning around them.
The SFX of Gravity: rendering space
"We knew we couldn’t move Sandra Bullock as we wanted to around the screen so we made her static – we put her in a rig," explained Wajsbrot.
"If she was actually spinning you would see the blood rushing to her face and this just doesn’t happen in zero gravity. So we put the lights and cameras on to robots – the same robot arms you get in the car industry."
But there was another problem: the cameras worked well with the robots but the lighting just wasn’t right.
According to Wajsbrot the lighting rig just wasn’t fast enough and it couldn’t go underneath the actors.
This was where solution number two came in. A 20 foot by 9 foot light box filled with 4,096 LED lights was assembled that would essentially encase the actors.
This light box could be controlled by the visual effects team and would align perfectly with the computer simulations that the actors’ faces would eventually be transposed on to.
For this to truly work, however, the lighting had to work perfectly in the previs – something that would take considerable grunt from the software Framestore was using.
"We usually use Renderman [made by Pixar] for previs but it’s a very specific language and Chivo would not understand it. It would have been hard to communicate to him how we were lighting the movie.
"So we changed to Mental Ray for pre-light [created by Nvidia] and Arnold [by Solid Angle] for the actual movie.
"This way we could speak with Chivo and Alfonzo in the same language and say ‘okay, add a block of light and we can do the same for reflections’. The light in this software reacts very similarly to real-life lighting – the way it bounces off of everything."
Not only did this type of rendering take up a huge amount of computational power – it would have taken 7,500 years if just one CPU was used in this process – it was uncharted territory for the team at Framestore. The synchronicity of camera, rigging, lighting and CG was unprecedented.
"It is probably the first movie where lighting was done in this way through a render, with every model given an incredible amount of detail. It works really well, though, because it had been planned so far ahead," said Wajsbrot.
"The CG lighting and the real lighting of the faces were done so that you believe they have been shot together. Usually you shoot on green screen with no real planning on the lighting and you try and match it up but this was the reverse process. We lit the CG and used this for when we lit the actors."
The result is a stunning piece of film tapestry that’s works thanks to the seamless stitching of visual effects and good old-fashioned acting. But even for such an effects-laden movie, Wajsbrot believes those who watch it (and have already watched it) will be surprised just how much of it was created by computer.
"People will be surprised – for instance, all of the suits are CG in the movie. We used simulation software to model the suits to make sure they had the right wrinkles. There was a team of 40 people working on only simulations of cloth for over a year – making everything as high-res as possible," he said.
And the subtle computer graphics didn’t end there.
"When people watch the movie they may think that the interior inside the ISS is a set and achieved with the actor on wires. Sandra is on wires but the whole interior is CG. For the inside we modelled more than 3,000 props."
Because the ISS has none of blackness of space – which takes far less time to render than colour – the renders for this part of the movie were a lot heavier and far more complex than the rest of the film.
Such reliance on CG did mean that that Gravity is original in another way. It is the first live-action 3D movie that isn’t strictly post converted in 3D nor shot in 3D, as Wajsbrot explains: "In my opinion Gravity is not a post-converted 3D movie because 95% of the frame is CG.
"It was rendered in stereo, then we post-converted the faces with a very accurate track. It was a very precise rendition. That’s why the stereo works so well because it was thought about a long time before the movie was made.
"The first time we read the script, 3D was part of the title and Alfonzo doing long shots helped with this as well. When you cut, cut, cut, it is hard to get the depth.
"The long takes are immersive and the fact it is space made the film work well in 3D."
Although the action of Gravity takes place 250km above us, its impact has had a huge effect back on earth, namely in London where Framestore is based. The numerous awards the company is getting for the effects means that the UK is finally seen as a powerhouse in the world of special effects.
"With Gravity we have showed that London can make a visual effects movie from beginning to end and do it by creating new techniques," said Wajsbrot.
"Before, London would use the tools from other companies but Gravity has changed the game. The scope of the movie meant that we had to create new technologies and a new way of making movies."
Gravity is out now on Blu-ray and Blu-ray 3D, courtesy of Warner Home Video. The movie has already become the fast-selling Blu-ray of all time, beating previous record holder Prometheus.