An algorithm for compression of bilevel images

This paper presents the block arithmetic coding for image compression (BACIC) algorithm: a new method for lossless bilevel image compression which can replace JBIG, the current standard for bilevel image compression. BACIC uses the block arithmetic coder (BAC): a simple, efficient, easy-to-implement, variable-to-fixed arithmetic coder, to encode images. BACIC models its probability estimates adaptively based on a 12-bit context of previous pixel values; the 12-bit context serves as an index into a probability table whose entries are used to compute p1 (the probability of a bit equaling one), the probability measure BAC needs to compute a codeword. In contrast, the Joint Bilevel Image Experts Group (JBIG) uses a patented arithmetic coder, the IBM QM-coder, to compress image data and a predetermined probability table to estimate its probability measures. JBIG, though, has not get been commercially implemented; instead, JBIGʹs predecessor, the Group 3 fax (G3), continues to be used. BACIC achieves compression ratios comparable to JBIGʹs and is introduced as an alternative to the JBIG and G3 algorithms. BACICʹs overall compression ratio is 19.0 for the eight CCITT test images (compared to JBIGʹs 19.6 and G3ʹs 7.7), is 16.0 for 20 additional business-type documents (compared to JBIGʹs 16.0 and G3ʹs 6.74), and is 3.07 for halftone images (compared to JBIGʹs 2.75 and G3ʹs 0.50)