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3D Artist
Dec
6

Creating Gravity’s Earth, stars, and lense flares

News & Features
by
stephen.holmes

Framestore’s compositing supervisor Anthony Smith gives us a breakdown of how the team created the Earth, stars and lense flares of Gravity

Creating Gravity's Earth, stars, and lense flares
 


For Framestore’s compositing department alone Gravity was a very unique show from the start; though perhaps this is unsurprising once you learn that the production of the film involved barely any green screens amongst elements such as the Light Box and detailed pre-vis process. “As well as compositing sitting at the end of the pipeline as we would be on a standard project, we were also involved in a few stages much earlier on to facilitate certain other procedures, which made it especially interesting from a compositor’s point of view,” explains compositing supervisor for Framestore Anthony Smith. Here, he tells us more about how the team, which for the majority of the project was made up of under 100 people, used NUKESilhouette and Mocha for everything from the Earth to the stars – and even the breath forming on visors.

 

The Earth

The layout process for the Earth was achieved entirely in NUKE. Alfonso Cuaron had already worked out a route loosely based on the orbit of the ISS so we knew where he wanted to be for each sequence and at what time of day. This was simply a globe with a piece of string taped around it and had the sequence names labeled at certain points.

To turn this into actual shots, we set up a system which allowed Tim Webber and Alfonso Cuaron to sit with members of the Earth compositing team – led by Kyle McCulloch – and creatively compose the Earth in NUKE to plan the route of travel for all of the exterior (and a few interior) shots. This involved creating an interface, which the compositor could use in one viewer to rotate the Earth under/above the pre-vis camera, while Tim Webber and Alfonso Cuaron could watch the output of the camera in another viewer with low resolution renders of the foreground characters and vehicles composited over it.

We were able to very subtly adjust the rotation of the Earth during the long shots without the viewer noticing, to ensure that we captured beautiful or interesting compositions throughout.
All of the Earth rotation data was exported from NUKE to the lighting TD’s, who could then use it for rendering.

Creating Gravity's Earth, stars, and lense flares

Stars

We constructed a celestial sphere from a database of the 120,000 or so most visible stars from the Earth that contained information about relative positions, velocities – which we converted into hues – and intensities. This meant we had the correct constellations in the correct positions. We then filled the remaining gaps with clouds of other stars created by duplicating the existing stars at lower exposures until we had over 30 million in our star field.

The starfield was completely controllable and rendered from NUKE by the compositing team. We were able to select any one of the main constellation stars and instantly rotate the celestial sphere so it was center of frame, or choose the date and time from any location on the Earth and it would rotate to the correct position. This ensured that we could keep continuity between shots, or creatively compose recognizable constellations into frame.

Creating Gravity's Earth, stars, and lense flares

Lens Flares

As part of the overall look of the film, how the lenses reacted to the light of the unobscured sun shining directly into them was hugely important, and we really wanted to use the real thing as no lens flare creation tool is as good. We used the motion control camera rig that was mounted to the Iris robot arm at Shepperton Studios to film an ultra bright LED in completely black conditions at the back of the lightbox stage. We did this with multiple exposures (to form an HDRI), with each lens used on the shoot, and with a particular camera move. With this footage, we built a tool that allowed the compositors to use a locator in 3D space and convert it into a 2D sun and lens flare render with a lens of their choosing. Given the matte of a 3D render it would even obscure the sun automatically when required!

Creating Gravity's Earth, stars, and lense flares

Conform

So that animation could continue to finesse the animation of the characters even after the shoot had taken place, we devised the ‘conform’ setup. It allowed us to track an object in the shot plate – often the helmet – and use this information, combined with a camera track, to lock the plate itself to a location in 3D space and allow it to be renderable from another camera. This meant that we could lock the astronauts’ faces into CG suits and the animators could continue to work on the character animation (and even their position and rotation in frame) and the plate would follow as if it were part of the animation rig.

Breath Elements

The breath elements on the visor – which was simply me breathing through a rolled up piece of black paper onto a pane of cold glass, and textured onto the visors in Nuke. The stunning animation, which was enhanced, based on the actors performances, even after the shoot took place. The Earth – so many locations, lighting conditions and weather systems, and it always looked beautiful. The breath elements in the cold Soyuz interiors – which were shot, line by line, by Framestore in their motion capture studio, on a Canon 5D, using a specially designed posable black tube with a compartment for dry ice, and with a mouth piece for someone to say the lines through.

Challenges and Successes

From the compositor’s perspective the pre-vis and pre-light were a huge advantage. It meant that the amount of relighting of shot footage that had to be done in the comp was kept to a minimum, and generally only overall grading was required to composite the heads into the helmets. Once the CG visors were composited over the live action helmet interiors, with the HUD, dirt and scratches, distortion, breath and reflections, the comps became very successful. Even doing rough comps on set at Shepperton, we could tell that some of the highly complex shots where Sandra was flipping and rolling around with direct sunlight on her face would work, just by dropping the face onto the pre-light renders.

For all but one of these set ups there was no green screen. The lack of it was mainly bad for the paint and roto team, who had a huge amount of work to do. They did a fantastic job rotoscoping around all of the helmets and faces, and an even better job rotoscoping Ryan when she was out her suit and painting out the many wires she was suspended from. The main difficulty for the interior compositors was Ryan’s hair, for which some particularly careful keying was required to pull mattes without the benefit of a green screen.

Creating Gravity's Earth, stars, and lense flares

Combined with our previous work, the emphatic success of Gravity so far has already allowed Framestore to be considered up there with any of the other leading visual effects facilities and I’m sure we will be involved in ground breaking projects in the future. As long as directors keep coming up with ideas that challenge visual effects artists and facilities to go beyond their creative limits and come up with things that are entirely new then the mould will keep getting broken and I’m sure Framestore will be there with each new development.

Discover more about how Framestore crafted the visuals behind Gravity  in 3D Artist Issue 62, on sale this week!