Hybrid compression algorithm for discrete-tone graphics processing

A hybrid algorithm for fast information lossless compression of discrete-tone images is presented. The algorithm is a combination of two algorithms: special RLE implementation, which can detect vertical and horizontal redundancy, and shift algorithm, which belongs to dictionary techniques. The shift algorithm replaces three bytes, which encode pixel color, by one byte reference to pixel with the same color, which was found earlier. Presented RLE implementation can detect three region types of pixels with the same color: vertical, horizontal lines and rectangles. Two combinations of hybrid algorithm with the known compression algorithms LZO and zlib (used on the second stage of compression) are researched. Results of practical comparison of combined algorithms among themselves and with other known algorithms are presented. As demonstrated by testing, combined algorithm, based on hybrid algorithm and zlib, gives an ability to significantly increase discrete-tone images compression ratio with an acceptable time cost.