Computer Animation Complete

All-in-One: Learn Motion Capture, Characteristic, Point-Based, and Maya Winning Techniques

Rick Parent, David S. Ebert, Mark V. Pauly, Darwyn Peachey, Ken Perlin, Hanspeter Pfister, Jason Sharpe, Mark R. Wilkins, Martin Wicke, Nicholas Woolridge, Steve Worley, David Gould, Markus Gross, Chris Kazmier, Charles John Lumsden, Richard Keiser, Alberto Menache, Matthias Müller, F. Kenton Musgrave

• Publisher: Morgan Kaufmann
• Year: 2009
• Print ISBN: 9780123750785
• eBook ISBN: 9780123785640
• Topic: Computer Science
• Subtopic: Computer Graphics
• Index: Computer Science

A compilation of key chapters from the top MK computer animation books available today - in the areas of motion capture, facial features, solid spaces, fluids, gases, biology, point-based graphics, and Maya. The chapters provide CG Animators with an excellent sampling of essential techniques that every 3D artist needs to create stunning and versatile images. Animators will be able to master myriad modeling, rendering, and texturing procedures with advice from MK's best and brightest authors. Divided into five parts (Introduction to Computer Animation and Technical Background, Motion Capture Techniques, Animating Substances, Alternate Methods, and Animating with MEL for MAYA), each one focusing on specific substances, tools, topics, and languages, this is a MUST-HAVE book for artists interested in proficiency with the top technology available today! Whether you're a programmer developing new animation functionality or an animator trying to get the most out of your current animation software, Computer Animation Complete: will help you work more efficiently and achieve better results. For programmers, this book provides a solid theoretical orientation and extensive practical instruction information you can put to work in any development or customization project. For animators, it provides crystal-clear guidance on determining which of your concepts can be realized using commercially available products, which demand custom programming, and what development strategies are likely to bring you the greatest success. - Expert instruction from a variety of pace-setting computer graphics researchers. - Provides in-depth coverage of established and emerging animation algorithms. - For readers who lack a strong scientific background, introduces the necessary concepts from mathematics, biology, and physics. - A variety of individual languages and substances are addressed, but addressed separately - enhancing your grasp of the field as a whole while providing you with the ability to identify and implement solutions by category.

PART 1

Introduction to Computer Animation

CHAPTER 1 Introduction

Rick Parent

Computer animation, for many people, is synonymous with big-screen events such as Star Wars, Toy Story, and Titanic. 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 SIGGRAPH¹ and on Sesame Street. Desktop computer animation is now possible at a reasonable 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 various venues are the cost, the image quality desired, and the amount and type of interaction allowed. This book 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 book 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 the following can be animated as well: the object’s shape, its shading parameters, its texture coordinates, the light source parameters, and the camera parameters.

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. The second is data-driven animation, in which live motion is digitized and then mapped onto graphical objects. The primary technology for data-driven animation is referred to as motion capture. The third is procedural animation, in which there is a computational model that is used to control the motion. Usually, this is in the form of setting initial conditions for some type of physical or behavioral simulation.

To set the context for computer animation, it is important to understand its heritage, its history, and certain relevant concepts. The rest of this chapter discusses motion perception, the technical evolution of animation, animation production, and notable works in computer animation. It provides a grounding in computer animation as a field of endeavor.

1.1 Perception

A picture can quickly convey a large amount of information because the human visual system is a sophisticated information processor. It follows, then, that moving images have the potential to convey even more information in a short time. Indeed, the human visual system has evolved to provide for survival in an ever-changing world; it is designed to notice and interpret movement.

It is widely recognized that a series of images, when displayed in rapid succession, are perceived by an observer as a single moving image. This is possible because the eye–brain complex has the ability, under sufficient viewing conditions and within certain playback rates, to create a sensation of continuous imagery from such a sequence of still images. A commonly held view is that this experience is due to persistence of vision, whereby the eye retains a visual imprint of an image for a brief instant once the stimulus is removed. It is argued that these imprints, called positive afterimages of the individual stills, fill in the gaps between the images to produce the perception of a continuously changing image. Peter Roget (of Thesaurus fame) presented the idea of impressions of light being retained on the retina in 1824 [1]. But persistence of vision is not the same as perception of motion. Rotating a white-light source fast enough will create the impression of a stationary white ring. Although this effect can be attributed to persistence of vision, the result is static. The sequential illumination of a group of lights typical of a movie theater marquee produces the illusion of a lighted object circling the signage. Motion is perceived, yet persistence of vision does not appear to be involved because no individual images are present. Recently, the causality of the (physiological) persistence of vision mechanism has been called into question and the perception of motion has been attributed to a (psychological) mechanism known as the phi phenomenon; the apparent motion is referred to as beta motion [2–4].

Whatever the underlying mechanism is, the result is that in both film and video, a sequence of images can be displayed at rates fast enough to fool the eye into interpreting it as continuous imagery. When the perception of continuous imagery fails to be created, the display is said to flicker. In this case, the animation appears as a rapid sequence of still images to the eye–brain complex. Depending on conditions such as room lighting and viewing distance, the rate at which individual images must be played back in order to maintain the perception of continuous imagery varies. This rate is referred to as the critical flicker frequency [5].

While perception of motion addresses the lower limits for establishing the perception of continuous imagery, there are also upper limits to what the eye can perceive. The receptors in the eye continually sample light in the environment. The limitations on motion perception are determined, in part, by the reaction time of those sensors and by other mechanical limitations such as blinking and tracking. If an object moves too quickly with respect to the viewer, then the receptors in the eye will not be able to respond fast enough for the brain to distinguish sharply defined, individual detail; motion blur results [6]. In a sequence of still images, motion blur is produced by a combination of the object’s speed and the time interval over which the scene is sampled. In a still camera, a fast-moving object will not blur if the shutter speed is fast enough relative to the object’s speed. In computer graphics, motion blur will never result if the scene is sampled at a precise instant in time; to compute motion blur, the scene needs to be sampled over an interval of time or manipulated to appear as though it were [7,8]. If motion blur is not calculated, then images of a fast-moving object can appear disjointed, similar to live action viewed with a strobe light. This effect is often referred to as strobing. In hand-drawn animation, fast-moving objects are typically stretched in the direction of travel so that the object’s images in adjacent frames overlap [9], reducing the strobing effect.

As reflected in the discussion above, there are actually two rates that are of concern. One is the playback or refresh rate – the number of images per second displayed in the viewing process. The other is the sampling or update rate – the number of different images that occur per second. The playback rate is the rate related to flicker. The sampling rate determines how jerky the motion appears. For example, a television signal conforming to the National Television Standards Committee (NTSC) format displays images at a rate of roughly 30 fps,² but because it is interlaced,³ fields are played at 60 fps to prevent flicker under normal viewing conditions [10]. In some programs (e.g. some Saturday morning cartoons), there may be only six different images per second, with each image repeatedly displayed five times. Often, lip-sync animation is drawn on twos (every other frame) because drawing it on ones (animating i...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• Contributing Authors
• Part 1: Introduction to Computer Animation
• Part II: Motion Capture Techniques
• Part III: Animating Substances
• Part IV: Other Methods
• Part V: Animating with MEL for MAYA
• Index