In thinking of virtual humans, it is natural to cast them in real films. Who wouldn´t be intrigued to see Adjani opposite Bogart in the romantic suspense of the season ? However, the reasons behind the increasingly complex techniques for portraying and directing virtual humans almost real enough to fool their mothers, are as much economic and educational as artistic. Virtual humans, in the large majority of applications, will be used to explore situations that have not yet happened. Couldn't we avoid a great deal of disappointment by seeing how we would look before having our hair done over, or cut differently ? More dramatically, wouldn't it relieve a lot of anxiety if candidates for plastic surgery could see their smiles before undergoing a face-lift or chin reconstruction ? Wouldn't be better to learn the anatomy and physiology of the human body or about problems in speech pathology by watching and manipulating synthetic actors? And why persist in using robots in ergonomics if we can simulate real people?|
The first computerized human models were created 20 years ago by aeroplane and car manufacturers. The main idea was to simulate a very simple articulated structure for studying problems of ergonomics. In the seventies, researchers developed methods to animate human skeletons, mainly based on interpolation techniques. Bodies were represented by very primitive surfaces like cylinders, ellipsoids or spheres. At the same time, the first experimental facial animation sequences appear.
The "Juggler" (1982) from Information International Inc. was the first realistic human character in computer animation; the results were very impressive; however, the human shape was completely digitized, the body motion had been recorded using 3D rotoscopy and there was no facial animation. The first 3D procedural model of human animation was used in producing the 12- minutes film DREAMFLIGHT ( 1982), one of the first to feature a 3D virtual human. In the mid- eighties, researchers started to base animation on the laws of physics. Dynamic simulation made it possible to generate complex motions with a great deal of realism. Even an ordinary human activity like walking is, however, too complex to be simulated by the laws of dynamics alone. Two people, even with the same physical characteristics, do not move in the same way. Even one individual does not move in the same way all the time. A behavioral approach to human animation will be necessary to lend credibility to such simulations.
But the main complexity in the animation of virtual human is the problem of integrating many techniques. True virtual humans should be able to walk, talk, grasp objects, show emotions and communicate with their environment. The face is a relatively small part of a virtual human, but it plays an essential role in communication. We look at faces for clues to emotions or even to read lips. It is a particular challenge to simulate these aspects. An ultimate objective therefore is to model human facial anatomy exactly, including its movements, with respect both to structural and functional aspects. Recent developments in facial animation include physically-based approximation to facial tissue and the reconstruction of muscle contractions from video sequences of human facial expressions. Problems of correlation between emotions and voice intonation have been also studied. Ensuring synchronization of eye motion, facial expression of emotion and the word flow of
a sentence, as well as synchronization among several actors, is at the heart of our new facial animation system at the University of Geneva.
The capability of animating virtual humans through a task-level language requires a deep understanding of how tasks should be specified. The process of interpreting natural language instructions involves subtle and sometimes unexpected connections between language and behavior. When the behavior is to be portrayed by a virtual human, various questions arise regarding the types and roles of planning, geometric reasoning, constraint satisfaction, human capabilities, and human motion strategies.