The emerging MPEG-4 standard supports the transmission and composition of facial animation with natural video. The new standard will include a facial animation parameter (FAP) set that is defined based on the study of minimal facial actions and is closely related to muscle actions. The FAP set enables model-based representation of natural or synthetic talking-head sequences and allows intelligible visual reproduction of facial expressions, emotions, and speech pronunciations at the receiver. This paper addresses the data-compression issue of talking heads and presents three methods for bit-rate reduction of FAPs. Compression efficiency is achieved by way of transform coding, principal component analysis, and FAP interpolation. These methods are independent of each other in nature and thus can be applied in combination to lower the bit-rate demand of FAPs, making possible the transmission of multiple talking heads over band-limited channels. The basic methods described here have been adopted into the MPEG-4 Visual Committee Draft and are readily applicable to other articulation data such as body animation parameters. The efficacy of the methods is demonstrated by both subjective and objective results.
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