Dictionary-type data compression for gray-scale images

We explore modifications of the LZ77 type dictionary compression algorithm so that it can compress gray-scale images efficiently. We consider the following modifications to the LZ77 compression: (1) Limiting the positions to start the pattern match in the search window to four neighboring pixels of the first pixel in the lookahead buffer. (2) Using an approximate matching. (3) Adaptively changing the lookahead buffer size. (4) Combination of approximate matching and exact matching using a non-greedy parsing algorithm. Our method is better than the UNIX compress and worst JPEG, and sometimes better than the best JPEG.