I.

Introduction

Animation, the simulation of on-screen movement produced by displaying successive images created with computer software and hardware.

II.

Persistence of Vision

The perception of on-screen movement is caused by a phenomenon called “persistence of vision”: when presented with a series of rapidly changing images, the human brain cannot process them fast enough to see each image separately and instead perceives a single continuous moving image. In standard cinematic films there are 24 frames (images) per second—24 fps. The set speed of television systems varies in different countries and is either 25 fps or 30 fps. Animation created for playback on a computer, CD-ROM, or DVD requires 14 fps or more for fluid movement and depends on the available random access memory (RAM) and speed of the computer’s processor or CD-ROM/DVD drive. At a low speed of 8 fps or less, the moving image will appear jerky or the illusion of movement may be lost altogether.

III.

The History of Computer Animation

A.

Origins

One of the first applications of “interactive” computer graphics was the US government’s SAGE air defence system of the mid-1950s; missiles and aircraft were detected by radar with their positions displayed on screen. Operators then selected targets by pointing at them with a light pen. The resulting tracking/interception calculations were relayed to command stations elsewhere.

B.

Early Computer Games

By the end of the 1960s, computer graphics had influenced some areas of the scientific community, but had not reached the general public. There were no commercially available video games; nor was there any CGI (computer-generated imagery) on television, or awareness of computer animation. The first interactive arcade game, Pong (simulated ping-pong), was introduced in the United States by Atari in November 1972. However, it was only in 1974 that Atari managed to bring down the retail price to a reasonable level and attract the home market worldwide. This was achieved by integrating features such as on-screen scoring and sound into a single computer chip (a microprocessor built from wafer-thin layers of silicon, chemicals, gases, and metals etched with a three-dimensional circuit that conducted electricity to execute a set of programmed instructions). The on-screen graphics consisted of a dotted vertical line representing the ping-pong net and simple geometric shapes representing bats and balls. Another early game, developed by Taito and published in the West by Midway, was Space Invaders, which became so popular that the word for video game machine in Japan and France became “space invader”.

C.

Growth of CGI

In 1981, Quantel’s introduction of its Paintbox machine (the first computer system dedicated to graphics for television) sparked a revolution in the television industry, causing the demand for TV graphics to grow exponentially so that by the early years of the 2000s practically every commercial or TV programme had some sort of graphic incorporated. The cult film, Tron (1982), produced by Disney and directed by Steven Lisberger, told the story of a programmer (Jeff Bridges) who is digitized and finds himself inside a computer, forced to play the computer games he, himself, has programmed. The film was a milestone in the use of CGI and an inspiration not only for those in the visual effects industry but for future artists and animators. Similarly, demand for computer animation and special effects grew in the film industry after the release of the 1993 film, Jurassic Park, by Steven Spielberg, in which life-like computer-generated dinosaurs roamed around on screen. The first full-length feature film created entirely using computer animation was Toy Story (1995), produced by Pixar and directed by John Lasseter. The 3-D toy characters were constructed from computer wireframe “meshes” and an in-house computer program called RenderMan put the surface drawings (“texture maps”) onto the wireframes. Animation “control points” were used to move/re-form sections of the wireframe—there were more than two hundred such points on the cowboy doll Woody’s face alone.

IV.

Computer- Versus Hand-Created Animation

Before computer and video technology, two-dimensional (2-D) animation was created either by hand drawing or painting on cels (transparent sheets of thin celluloid) or paper, or by the stop-frame technique of moving a three-dimensional (3-D) model, shooting one or two frames, and repeating the process. In 2-D, a frame could consist of a “sandwich” of up to seven cels, each with painted sections of imagery, as well as a background drawn or painted on paper. A key animator would draw the “extreme” positions of a character (called “key frames”) and other artists would draw the “in-betweens”. Each single-frame sandwich of cels would then be photographed by a film camera with a stop-frame facility, before development and projection. Two- and three-dimensional software mimic many of these traditional processes. For example, an “onion skinning” facility, like cels, enables the animator to view a series of images, one behind the other; also, in the processes of “key framing” and “tweening”, the animator creates key frames and the computer generates some types of in-betweens. Traditional animation may still find use in short “art” productions, but increasingly digital aids are used to shorten or enhance the process, such as when hand-created images are scanned into the computer. Digital video has largely replaced film. Typical 3-D effects, easily created with a computer, may be too time consuming to be created by hand; for example, complex “camera” movement, lighting effects, realistic simulation of hair, fur, flowing water, fire, and other natural phenomena.

V.

Methods of Creating and Storing Computer Animation

The methods by which computer animation may be created and stored depend on the animation’s final display output: website, computer game, DVD/TV, HD (high definition), full or part screen PC, cinema screen, as well as the style and complexity of the image required. For example, simple cartoon-style images (commonly “2-D” animation) require less storage space when created with vector-based software, which records instructions by the user and reconstructs the image on screen later. A further advantage of this method is that it is “resolution independent”; that is, the picture can be magnified without the “pixilation” incurred when a bitmap image is enlarged. A bitmap consists of a matrix (right-angled criss-crossing rows and columns) of pixels (short for “picture elements”), which vary in colour and brightness—the little coloured rectangles or squares that become visible when the image is greatly enlarged. For scenes requiring photorealistic imagery with subtle tonal gradations and unlimited colours (commonly “3-D” animation or special effects), bitmap storage is more suitable.

Character creation is no longer just the art of 2-D animators. John Lasseter, head of Pixar Animation Studios, demonstrated this when he used early 3-D software to portray endearing character interaction between two table lamps in the short film Luxo Jr (1986). A useful aid for 3-D character animation is the technique of motion capture, first used entirely in a film by Robert Zemeckis in The Polar Express (2004). This entails fitting electronic gadgetry to humans or animals, who perform the action required. Data is then collected and translated by animation software into the movement of the given computer characters. Another method is rotoscoping, a process that freezes each conventionally shot film frame and converts it into a computer image. The artist/animator can then rework the image digitally to achieve a desired effect.

Computer animation may be produced in two ways. It can be created in simulated time, when each frame is designed in advance and may take minutes or even hours to “render” (that is, form and colour), before being rapidly displayed to maintain the illusion of movement. Alternatively it can be produced in real time, with the computer drawing and colouring the animated scenes “on the fly” as the user watches or interacts. This method is important for applications such as 3-D games, where it is impractical to predict all the scenes that may be needed for an interactive 3-D environment. Such animation requires fast computer hardware plus real-time 3-D rendering software, and the image quality is unlikely to match that of pre-rendered animation, although it is improving all the time. There are many different specialist 2-D and 3-D software packages available, tailored to specific needs.