Adaptive entropy-coded subband coding of images

Recently, subband coding has been the subject of rather extensive investigation in the area of image coding because of its potential advantages over fullband coding. However, most of the work on subband coding (SBC) has been based on level-constrained design of the embedded quantizers. In this paper, we describe a new design approach, called 2-D entropy-constrained subband coding (ECSBC), based upon recently developed 2-D entropy-constrained vector quantization (ECVQ) and 2-D entropy-constrained predictive vector quantization (ECPVQ) schemes. The output indices of the embedded quantizers are further compressed by use of noiseless entropy coding schemes, such as Huffman or arithmetic codes, resulting in variable-rate outputs. We also describe an adaptive buffer-instrumented version of 2-D ECSBC, called 2-D ECSBC/AEC, for use with fixed-rate channels which completely eliminates buffer overflow/underflow problems. This adaptive scheme is shown to achieve performance quite close to the corresponding ideal 2-D ECSBC system.