In this paper, we address the problem of the efficient encoding of object boundaries. This problem is becoming increasingly important in applications such as content-based storage and retrieval, studio and television postproduction, and mobile multimedia applications. The MPEG-4 visual standard will allow the transmission of arbitrarily shaped video objects. The techniques developed for shape coding within the MPEG-4 standardization effort are described and compared first. A framework for the representation of shapes using their contours is presented next. Such representations are achieved using curves of various orders, and they are optimal in the rate-distortion sense. Last, conclusions are drawn.

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A major problem in object oriented video coding and MPEG-4 is the encoding of object boundaries. In our previous work, we presented efficient methods for the lossy encoding of object boundaries which were optimal in the rate distortion sense. In this paper, we extend our work to utilize both the original image and an initial segmentation to obtain the optimal shape representation based on the criteria we impose. The boundary detection and encoding problems are considered simultaneously. If there is low confidence on the location of the boundary, a large approximation error is allowed when encoding the boundary and vide versa. Experimental results demonstrate the effectiveness of the proposed algorithm.