IEEE Trans. on Image Proc. (Submitted, June 1997)

Title: Image Subband Coding Using Context-Based Classification and Adaptive Quantization
Authors: Y. Yoo, A. Ortega, and B. Yu
Where: IEEE Transactions on Image Processing, Submitted, Jun. 1997
Abstract: Adaptive compression methods have been a key component of many of the recently proposed subband (or wavelet) image coding techniques. This paper deals with a particular type of adaptive subband image coding where we focus on the image coder's ability to adjust itself on the fly to the spatially varying statistical nature of image contents. This backward adaptation is distinguished from more frequently used forward adaptation in that forward adaptation selects the best operating parameters from a pre-designed set and thus uses considerable amount of side information in order for the encoder and the decoder to operate with the same parameters. Specifically, we present a backward adaptive quantizer by introducing a new context-based classification technique which classifies subband coefficients based on the surrounding quantized coefficients. We couple this classification with on-line adaptation of the quantizer used within each class. The quantizers themselves are simple scalar uniform threshold quantizers and we demonstrate that classification yields excellent results in terms of objective quality, in particular at very low rates. Our results are comparable, or superior for some images, to all published state-of-the-art coders.