Symbol Matching Based Facsimile Data Compression

Abstract

Presented here is an efficient facsimile data coding scheme (CSM) which combines an extended run-length coding technique with a symbol recognition technique. The CSM scheme first partitions the data into run-length regions and symbol regions. The run-length regions are then coded by a modified Interline Coding technique, while the data within the symbol region is further subpartitioned into regions defined as symbols. A prototype symbol library is maintained, and as each new symbol is encountered, it is compared with each element of the library. These comparisons produce a signature for the new symbol. A tolerance threshold is used to evaluate the "goodness" of the comparison. If the tolerance threshold indicates a matching symbol, then only the location and the library address need be transmitted. otherwise the new symbol is both transmitted and placed in the library. For finite sized libraries a scoring system determines which elements of the library are to be replaced by new prototypes. Simulation results are demonstrated for both CCITT and Xerox standard documents. In all cases the CSM compression ratio exceeds the best published run-length technique by a factor of at least two, for pages that are predominately test. For non-test predominate pages, the CSM scheme is at least as good as the best published run-length technique.