Scalable ideal-segmented chain coding

We present an optimal chain-code-like representation to code contour shapes; in addition, this representation can be easily extended to a scalable form which structures shape data as the base layer followed by two enhancement layers. A lossy coding scheme is also presented for low-bit-rate applications. Compared with the block-based CAE (context-based arithmetic encoding) method in MPEG-4 and DCC (differential chain coding) with an arithmetic coder, our method not only has a higher compression ratio with fewer computation steps, but also can be applied to layered transmission. The scalability achieved by our scheme can be recognized both spatially and quality-wise. Compared with other scalable shape coding methods, our scheme is simple but more efficient than progressive polygon encoding methods. In case of a base layer with distortion Dn=0.02, our scheme saves about 20-30% of the number of bits, that is, we have a smaller size base layer, which is important in layered transmission.