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Optimal Block-Adaptive Image Coding with Constrained Bit-Rate

A novel technique is presented for block coding of images where the total number of bits per image is constrained and an optimal (or near-optimal) allocation of bits to each block is determined adaptively. The input image is segmented into non-overlapping blocks and each block is coded by one of a finite set of predesigned block quantizers covering a range of bit-rates. For the i-th block, a rate function Ri(L,) and a distortion function Di(Li) can be tabulated for each block quantizer Li . An optimal quantizer allocation algorithm is used to select a particular quantizer for each block. The objective is to minimize the distortion of the entire image under the constraint on the total number of bits for the image. A block-adaptive coder based on the DCT and vector quantization with a multistage structure was designed to implement this technique. Computer simulations demonstrate the effectiveness of the new algorithm.