Coding of two-level pictures by pattern matching and substitution

A pattern matching approach is proposed for coding of two-level pictures. Patterns, which are either symbols such as characters, or fractions of black regions, such as line segments, are extracted from the facsimile. They are compared and matched to already transmitted patterns, called library patterns. If a correct match is detected, only the position of the pattern and the identification of the matching library pattern are transmitted. If a pattern does not match any library pattern, it is added to the library and its binary description is transmitted. Compared to conventional two-dimensional codes, the compression is often doubled and is sometimes 4.5 times higher. Compared to a symbol-matching coding technique,² the compression has increased by 20 to 80 percent, depending upon the document.