Optimal shape coding under buffer constraints

In this paper, we derive an optimal rate control algorithm for shape coding as defined in the forthcoming MPEG-4 international standard. The current MPEG-4 shape coding scheme consists of two steps: first, distortion is introduced by down and up scaling; then, context-based arithmetic encoding is applied. Since arithmetic coding is “lossless”, the down up scaling step is considered as a virtual quantizer. We first formulate the buffer-constrained adaptive quantization problem for shape coding, and then propose an algorithm for the optimal solution under buffer constraints. Experimental results are given using an MPEG-4 shape codec