MPEG-4 standardized methods for the compression of arbitrarily shaped video objects

MPEG-4 is the most recent standard for audio-visual representation to be pu blished by the International Organization for Standardization, One of the m any new features of MPEG-4 is its ability to represent two-dimensional vide o objects of arbitrary shape. For this purpose, MPEG-4 uses the conventiona l motion-compensated discrete cosine transform syntax for color/texture cod ing and augments this with an explicit compressed representation of the vid eo object's shape. This paper is intended as a tutorial in the means of enc oding and decoding arbitrarily shaped video objects as specified by MPEG-4. The major emphasis of the paper is on explaining the compression technolog y associated dth the normative shape representation, i.e., block-based cont ext-based arithmetic encoding, but some new aspects associated with arbitra rily shaped texture coding are also highlighted, The MPEG-4 specifications are presented in an informal may, and the motivations underlying the algori thm are clarified. In addition, effective methods are suggested for perform ing many of the nonnormative encoding tasks, and several encoding performan ce tradeoffs are illustrated.