COMPRESSION OF BINARY IMAGES BY COMPOSITE METHODS BASED ON BLOCK CODING

Composite methods for compressing binary images are studied. Hierarchi cal block coding is the main component in all of them. An attempt is m ade to increase the compression by augmenting the block coding by pred ictive coding and bit row reordering. The purpose is to increase the n umber of white pixels and all-white blocks. An error image is construc ted 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.