【地心引力】Creating Gravity’s Earth, stars, and lense flares（创建重力的地球，恒星和透镜耀斑）
Framestore’s compositing supervisor Anthony Smith gives us a breakdown of how the team created the Earth, stars and lense flares of Gravity
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 previs 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 NUKE, Silhouette and Mocha for everything from the Earth to the stars – and even the breath forming on visors.
【翻译】对于Framestore的合成部门从一开始就把《地心引力》独立成一个非常独特的项目，虽然一旦你学会了制作电影所涉及的几乎没有任何绿屏之间的元素，如灯箱和详细的预VIS过程之后，也许这些都不足为奇的。 “除了在标准的项目流程中合成被安排到了流程的最后，我们也参与到了几个更早阶段上，以方便其他某些流程，这使得它特别是从一个排字的点有趣的， “Framestore合成总监安东尼·史密斯说到。在这里，他会告诉我们更多关于团队如何，这对于广大工程是由不少于100人，使用NUKE，Silhouette和Mocha制作一切从地球到星星和护目镜甚至人的呼吸。
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.
【翻译】为了把它变成实际拍摄中，我们建立了一个系统，允许添韦伯和阿方索关键字句坐下来与地球合成团队的成员 – 率领凯尔麦卡洛克 – 创造性地构成了地球NUKE计划出行的所有途径外部（和一些内部）的镜头。这包括创建一个接口，它的合成器可以用在一个浏览器转动地球下/上预VIS摄像头，而蒂姆·韦伯和阿方索关键字句可以看相机的另一个浏览器与低分辨率输出呈现前景人物和车辆合成了它。
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.
所有地球自转的数据是从NUKE出口到 lighting TD’s，谁便可以使用它进行渲染。
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.
【翻译】我们转换成色调 – – 和强度，我们从地球的120,000左右最明显的恒星，大约含有相对位置，速度信息的数据库构建的天球。这意味着我们必须在正确的位置正确的星座。然后，我们填补留下的空隙与云通过复制现有的星星较低的风险，直到我们有3000多万在我们的星域创建的其他星星。
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.
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!
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.
使动画能够继续巧妙的人物即使在拍摄已发生的动画，我们设计了“符合”的设置。它使我们能够在拍摄板跟踪对象 – 经常头盔 – 并使用该信息，结合一个照相机磁道，以锁定所述板本身的位置在3D空间中，并使其从另一摄像机渲染。这意味着我们可以锁定宇航员的面孔进入CG场景和动画师可以继续工作，对角色动画（甚至是它们的位置和在框架旋转）和板将遵循犹如动画钻机的一部分。
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.
【翻译】头罩上的气息元素 – 无非是我的呼吸，它通过卷起一张黑纸到冷玻璃的窗格和质感上的核弹的遮阳板。令人惊叹的动画，这是增强的，基于角色的表现，即使在拍摄发生。地球 – 所以许多地方，照明条件和天气系统，它总是长得很漂亮。在寒冷的联盟内饰气息的元素 – 这被枪杀，一行行，通过的Framestore在他们的动作捕捉工作室，在佳能5D，采用特殊设计的posable黑色管带隔间的干冰，并带口的一块有人通过说行。
Challenges and Successes（挑战与成功案例）
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.
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.