Hierarchical predictive approach to image coding

Properties related with statistical redundancy of hierarchical image codes have been unveiled recently, allowing for a potential high bit rate reduction in storage or transmission. Appropriate schemes can be developed to take advantage of these properties, either for lossless or lossy applications. Here, a predictive approach for hierarchical line encoding is presented, giving rise to a two step procedure (hierarchical plus predictive). Both predictor and quantiser have been adapted to the different pixel weight within the hierarchical code; the selective quantiser has so been developed as a function of code outgrowth layer. Zero bit quantisation is also used to reduce bit rate in the large uniform areas of last code layers. Performance of the proposed scheme has been tested on a significative set of images, behaving well even with high entropy pictures. Results offer encoding at a bit rate around 0.5 bit/pixel, while subjective quality is still kept high.