LZ77 and LZ78

LZ77 and LZ78 are the names for the two lossless algorithms published in papers by Abraham Lempel and Jacob Ziv in 1977 and 1978. These two algorithms form the basis for most of the LZ variations including LZW, LZSS and others. They are both dictionary coders, unlike minimum redundancy coders or run length coders. The LZ77 algorithm works by keeping a history window of the most recently seen data and comparing the current data being encoded with the data in the history window. What is actually placed into the compressed stream are references to the position in the history window and the length of the match.