EFFICIENT HALFTONE IMAGE COMPRESSION

An image compression algorithm (10) and complementary decompression algorithm (20) are disclosed. The compression algorithm (10) maintains a set of reference points (610, 611, 612 and 613), each reference point having a predetermined spatial relationship with a current pixel (600). An adjustment along scanlines of the reference points is determined. Each of the reference points (611, 612 and 613) is then adjusted by the determined adjustment. A search for a match between one of the strings of consecutive previously scanned pixels including one of the adjusted reference pixels and the string of consecutive pixels including the current pixel is then conducted, and if a match is found, then an identifier for the reference pixel included in the match and the length of the matching string of consecutive pixels are encoded to an output stream.