Efficient encoding and decoding algorithms for variable-length entropy codes

Successive versions of the MPEG and JPEG coding standards have been widely adopted for compression of moving pictures and still images. Variable-length codes (VLC) such as Huffman codes are generally employed within the frameworks of these standards to achieve optimal coding efficiency in the entropy coding stage. Conventional table look-up encoding/decoding techniques for VLC are inefficient in memory usage. This is a particularly important consideration for hand-held devices, such as cellular phones with image reception and processing capabilities. The authors present a series of efficient and simple algorithms for VLC encoding and decoding based on a pointer look-up approach. They present both software and hardware implementations of these algorithms, and a comparison of memory requirements associated with the pointer look-up and conventional techniques.