COMPRESSION OF BINARY IMAGES BY COMPOSITE METHODS BASED ON BLOCK CODING

Composite methods for compressing binary images are studied. Hierarchical block coding is the main component in all of them. An attempt is made to increase the compression by augmenting the block coding by predictive coding and bit row reordering. The purpose is to increase the number of white pixels and all-white blocks. An error image is constructed from the differences between the predicted and original values of the pixels. The error image is then coded by hierarchical block coding, in which Huffman coding is used to encode the different bit patterns at the lowest level of the hierarchy. In the method, the global level dependencies are thus handled by block coding and the local pixel-to-pixel dependencies by Huffman coding. (C) 1995 Academic Press, Inc.