I. Introduction
IN RECENT YEARS, the interest in object-based coding has grown. This is partly due to the creation of the MPEG-4 standard [1], which allows for arbitrarily-shaped objects to be coded. The key technical development that allows object-based functionality to be achieved is an efficient and flexible means of coding the shape of an object. The MPEG committee has adopted a context-based arithmetic encoding (CAE) algorithm for this purpose [2]. With this coding scheme, the binary shape data may be coded at multiple scales, which allows for the shape coder to achieve a trade-off between rate and distortion.