Introduction - Computer Animation: Algorithms and Techniques - page 1

CHAPTER

1

Introduction

Computer animation, for many people, is synonymous with big-screen events such as Star Wars , Toy
Story , and Avatar . But not all, or arguably even most, computer animation is done in Hollywood. It is
not unusual for Saturday morning cartoons to be entirely computer generated. Computer games take
advantage of state-of-the-art computer graphics techniques and have become a major motivating force
driving research in computer animation. Real-time performance-driven computer animation has
appeared at SIGGRAPH 1 and on Sesame Street . Desktop computer animation is now possible at a rea-
sonable cost. Computer animation on the Web is routine. Digital simulators for training pilots, SWAT
teams, and nuclear reactor operators are commonplace. The distinguishing characteristics of these var-
ious venues are the cost, the image quality desired, and the amount and type of interaction allowed. This
topic does not address the issues concerned with a particular venue, but it does present algorithms and
techniques used to do computer animation in all of them.
Computer animation , as used here, refers to any computer-based computation used in producing
images intended to create the perception of motion. The emphasis in this topic is on algorithms and
techniques that process three-dimensional graphical data. In general, any value that can be changed
can be animated. An object's position and orientation are obvious candidates for animation, but all
of the following can be animated as well: the object's shape, its shading parameters, its texture coor-
dinates, the light source parameters, and the camera parameters.
This topic is organized as follows. To lay a firm foundation for the rest of the topic, Chapter 2 surveys
the technical background of computer graphics relevant to computer animation. This includes the fun-
damental geometric transformations and associated representations of graphical data. It can be skipped
by those well versed in the mathematics of the computer graphics display pipeline. Chapters 3-11 cover
various computer animation algorithms and techniques: Chapters 3-5 deal with directly specifying
motion (kinematics), Chapter 6 covers digitizing motion (motion capture), Chapters 7 and 8 consider
physically based animation (dynamics), and Chapters 9-11 concentrate on (mostly human) figure
animation. Finally, Chapter 12 surveys some modeling techniques that have been used in computer
animation. The appendices provide ancillary material. Appendix A covers rendering issues that are
relevant for animation, and Appendix B provides detail of the mathematics used in the text.
In considering computer animation techniques, there are basically three general approaches to
motion control. The first is artistic animation in which the animator has the prime responsibility
for crafting the motion. The foundation of artistic animation is interpolation. Various animation

1 SIGGRAPH is the Association for Computing Machinery's (ACM) special interest group on computer graphics. The ACM
is the main professional group for computer scientists.