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Joe Letteri, Oscar-winning   co-creator of Gollum on screen,   looks at the evolution[i]   of computer animation as the next instalment[ii]   of The Hobbit trilogy[iii]   reaches cinemas.

From   the beginning, computer animation has had the ability to engage[iv]   viewers by giving artists a way to mix[v]   reality with fantasy. Early   film examples 【such as the stained-glass[vi]   knight[vii]   in Barry Levinson’s 1986 Young Sherlock   Holmes and the ‘water tentacle[viii]’   in James Cameron’s 1989 The Abyss 】offered a glimpse[ix]   of the potential of this new art form to create memorable characters.   That became immediately apparent in Cameron’s later Terminator 2 (1991). He took an already great idea for a   character (a terminator robot) and turned it in a new and unexpected   direction: the shape-shifting T-1000 liquid-metal terminator.

Computer   animation is a natural extension of hand-drawn methods developed during the   early-twentieth-century golden age of ‘cel’ animation[x]   ushered[xi]   in by Walt Disney, in which a series of images is played back at speed to   give the illusion[xii]   of life. Just as we do today,   animators used a variety[xiii]   of reference techniques to capture[xiv]   the essence of organic movement. Snow White’s dance with the dwarves in   Disney’s 1937 film was created by matching the movements of a live, filmed   dancer, using a technique called roto- scoping[xv]   — in the most basic terms, tracing the motion from a film one frame[xvi]   at a time. This technique, although now slightly more sophisticated[xvii]   in its application, is still in use.

Take   dinosaurs, for example. I was fortunate to begin my career at the US visual-effects   company Industrial Light & Magic, then in Marin County, California, as it   was gearing up[xviii]   to create the computer-generated dinosaurs for Steven Spielberg’s 1993 Jurassic Park. Naturally, we all   thought that roto-scoping dinosaurs would be a   great idea, but unfortunately that was out of the   question[xix].   Instead, we studied elephants to understand weight, and lizards, other   reptiles and birds to get some ideas about how dinosaurs of different sizes   might have moved. Digital animators did motion studies, copying the movement   of these animals frame by frame until they could synthesize a convincing idea   of dinosaur movement.

Two   years later, computer animation took another big step forward with the astounding[xx]   success of Pixar’s Toy Story.   Software was becoming sophisticated enough to tackle the creation of a   character’s performance. In traditional animation, a lead animator sets key   frames or poses for a character and junior animators draw the ‘in-betweens’   from pose to pose. Now, artists could use the computer to do that. Pixar   proved that three-dimensional computer animation could be used to create an   entire film.

In   2001, I joined Wellington-based visual-effects company Weta Digital to work   with Peter Jackson on The Lord of the   Rings trilogy, inspired[xxi]   in large part by the chance to create the character Gollum. With Gollum, we   used the then relatively new technique of performance capture — effectively,   an extension of rotoscoping. But instead of looking at an actor from a single   point of view and matching the form of the motion, we looked at his   performance using dozens of cameras simultaneously and matched the motion’s underlying[xxii]   dynamics.

Andy Serkis,   who performed Gollum, wore a special suit with reflective markers to show the   key positions of his joints. From the multiple cameras, we could calculate   his skeleton’s position at every frame as he performed.

The   problem with trying to capture facial motion is that there are no joints,   apart from the jaw, that have movements you can track. So for Jackson’s 2005 King Kong, Weta came up with a   different technique. Again with Serkis, we glued small reflective markers all   over his face. By using these to track the changes in skin position and   tension as Andy performed, we could compute what his muscles were doing underneath[xxiii].   Then we built Kong so that he had the same facial-muscle layout as Andy, and   used Andy’s muscle movements to drive Kong’s facial performance.

This   breakthrough meant that we could now capture an actor’s performance in its entirety[xxiv].   This became important for Weta’s next film, James Cameron’s Avatar (2009), for which we made one   important modification[xxv].   Each actor wore a helmet that filmed their facial movements; we then extracted[xxvi]   the performance data from each frame and used a ‘facial action coding system’   solver to translate the movements into muscle activations[xxvii].   The knowledge of which muscles are activated in a facial expression informed   our activation of the corresponding muscles in the digital characters. In   addition, this process allowed the director to see the actors live through a virtual[xxviii]   camera as they were instantly transformed into their Na’vi characters moving   through the world of Pandora.

Digital   characters also have to appear realistic in their surroundings, whether that   is a photographed environment or a complete digital creation such as the   jungles of Pandora. So we looked to understand how light and materials   interact in nature. One of the best examples of this interaction is subsurface scattering[xxix].   We first developed a technique to replicate[xxx]   this mechanism of light transport to create the translucency[xxxi]   of Gollum’s skin, leveraging[xxxii]   pioneering research by computer-graphics specialist[xxxiii]   Henrik Wann Jensen and his colleagues at Stanford University in California.

Realistic   animation also depends on knowledge of how skin, muscles and hair move   independently of a character’s performance. These secondary motions are   achieved through intensive simulations[xxxiv]   that compute all of the mass[xxxv],   dynamics[xxxvi],   tensions[xxxvii]   and interaction of each part of the body as a character moves. The simulations help to   create the complex visual cues that the human brain processes when taking in   an image. They   also ensure[xxxviii]   that the physiology of creatures (real or fantastical) has a ground truth and   is believable. Combining this new level of detail with motion-captured   performances of talented actors has enabled computer-animated characters to   become lead actors.

The   following year saw all of these developments come   full circle[xxxix]   when we were able to once again present Gollum in Peter Jackson’s The Hobbit: An Unexpected Journey.   This new Gollum benefited from a much more detailed   digital model, new subsurface scattering techniques, and all of the advances we have made   in the past ten years. If you watch closely, you will see the muscles   moving under his skin and the light refracting[xl]   in his eyes. And you will get a glimpse of the worlds we can create from the   mix of all this art and science.

奥斯卡获奖影片《屏幕上的咕噜》(Gollum on screen)的创作者之一乔·莱特里(Joe Letteri)在《霍比特人》(Hobbit)三部曲的下一部上映之际，展望了电脑动画的发展。

从一开始，电脑动画就能让艺术家们将现实与幻想结合起来，从而吸引观众。早期的电影就有这样的例子，如1986年巴里·莱文森(Barry   Levinson)拍摄《年轻的夏洛克·福尔摩斯》(Young   Sherlock Holmes)中的彩色玻璃骑士，以及詹姆斯·卡梅隆(James Cameron) 1989年拍摄的《深渊》(the Abyss)中的“水触须”， 这些使我们得以一窥这种新艺术形式创造令人难忘角色的潜力。这一点在卡梅隆后来的《终结者2》(1991)中表现得很明显。他为角色(终结者机器人)想出了一个已经很不错的主意，并把它转向一个全新的、意想不到的方向:可以变形的T-1000液态金属终结者。

电脑动画是手绘方法的自然延伸，这些方法在二十世纪早期由迪斯尼引领的“单帧”动画的黄金时代发展起来，即一系列的图像被快速回放，给人以真实景象的幻觉。正如我们今天所做的，动画师使用了各种各样的引用技术来捕捉有机运动的本质。迪斯尼1937年的电影《白雪公主与小矮人》中，白雪公主与小矮人的舞蹈动作是通过匹配一个现场拍摄的舞者的动作而创造出来的，使用了一种旋转照相术的技术——用最基本的术语来说，就是在一帧一帧地追踪电影中的动作。这种技术虽然目前在应用上稍微复杂一些，但仍然在使用中。

以恐龙为例。我很幸运能够在美国视觉特效公司Industrial Light & Magic（位于加利福尼亚州马林县）开始我的职业生涯，当时这家公司正准备为史蒂文•斯皮尔伯格(Steven Spielberg) 1993年的《侏罗纪公园》(Jurassic   Park)制作电脑制作的恐龙。当然，我们都认为旋转拍摄恐龙是一个好主意，但遗憾的是，这是不可能的。相反，我们通过研究大象来了解体重，通过研究蜥蜴、其他爬行动物和鸟类来了解不同体型的恐龙是如何移动的。数字动画师做运动研究，一帧一帧地复制这些动物的运动，直到他们能够合成一个令人信服的恐龙运动的想法。

两年后，电脑动画又向前迈进了一大步，皮克斯的《玩具总动员》取得了惊人的成功。软件变得足够复杂可以处理角色的表现。在传统动画中，首席动画师为角色设置关键帧或摆姿势，初级动画师则绘制从一个姿势到另一个姿势   的“中间部分”。现在，艺术家们可以用电脑来做到这一点。皮克斯证明了三维电脑动画可以用来制作整部电影。

2001年，我加入了总部位于韦林顿的视觉特效公司Weta Digital，与彼得·杰克逊(Peter Jackson)合作拍摄《指环王》(Lord of The Rings)三部曲，很大程度上是因为有机会创造出咕噜(Gollum)这个角色。对于咕噜，我们使用了当时相对较新的表演捕捉技术——有效地扩展了旋转照相术。但是，我们不是从单一的角度看一个演员，并匹配其动作形式，而是同时使用几十个摄像机观察他的表演，并匹配动作的潜在动态表现。

扮演咕噜的安迪·瑟金斯(Andy Serkis)穿着一套带有反光标记的特殊服装，以显示他关节的关键位置。从多个摄像头中，我们可以计算出他表演时，他每一帧的骨骼位置。

试图捕捉面部动作的问题在于，除了下巴，没有任何关节有你可以追踪的动作。因此，在杰克逊2005年的《金刚》中，维塔采用了一种不同的手法。我们又用了瑟金斯，在他脸上粘了一些小的反光标记。通过使用这些东西来跟踪安迪表演时皮肤位置和张力的变化，我们可以计算出他的肌肉在下面做什么。然后我们做了金刚，让他有和安迪一样的面部肌肉布局，用安迪的肌肉运动来驱动金刚的面部表现。

这一突破意味着我们现在可以完整地捕捉演员的表演。这对维塔（Weta）的下一部电影，詹姆斯·卡梅隆的《阿凡达》(2009)很重要，我们对它做了一个重要的修改。每个演员都戴着头盔，记录他们的面部动作;然后我们从每一帧中提取表演数据，并使用“面部动作编码系统”解算机将动作转化为肌肉活动。面部表情中哪些肌肉被激活的知识告诉了我们数字人物中相应肌肉的激活数据。此外，这个过程让导演可以通过虚拟摄像机看到演员们的表演，演员可以瞬间被转换成电影中呈现的纳威人，在潘多拉星球上穿梭。

数字角色也必须在他们的环境中表现得很真实，无论是一个被拍摄的环境还是一个完整的数字创造环境，比如潘多拉的丛林。所以我们试图理解光和材料在自然状态下如何相互作用。这种相互作用的最佳例子之一是次表面散射。我们首先利用计算机图形学专家Henrik Wann Jensen和他在加州斯坦福大学的同事的开创性研究，开发了一种技术来复制这种光传输机制，以创造咕噜姆皮肤的半透明。

逼真的动画也依赖于皮肤、肌肉和头发如何独立于角色的表现而运动的知识。这些次级运动是通过密集的模拟来实现的，模拟计算了角色移动时身体各部分的质量、动力学、张力和相互作用。这些模拟有助于创建当人类大脑处理图像时要用到的复杂的视觉线索。他们还确保生物的生理学(真实的或虚幻的)有一个基本的真理，是可信的。将这种新水平的细节与天才演员的动作捕捉表演相结合，使电脑动画人物成为主角。

在接下来的一年里，当我们能够再次在彼得·杰克逊的《霍比特人:意外之旅》中呈现咕噜时，所有这些发展又兜个圈回到了原点。这个新的咕鲁得益于一个更详细的数字模型，新的次表面散射技术和我们在过去十年中取得的所有进步。如果你仔细观察，你会看到他皮肤下的肌肉在运动，光线在他眼睛里折射。你会看到我们可以从所有这些艺术和科学的混合中创造出的世界。