LempelZiv

Lempel-Ziv refers to a family of lossless data compression algorithms developed by Abraham Lempel and Jacob Ziv in the 1970s. The original work introduced two related schemes, LZ77 and LZ78, and the broader family has spawned numerous variants and improvements used in modern compression tools.

LZ77, also known as the sliding-window method, encodes data by replacing repeated strings with references to earlier occurrences within a moving window. Each reference specifies a distance (how far back) and a length (how many symbols). A literal may follow the reference to terminate the match. This approach enables adaptive compression without a separate dictionary, and it underpins many contemporary algorithms and formats, such as DEFLATE.

LZ78 builds a dictionary of progressively longer phrases as data is scanned. Each encoded item consists of an index to a dictionary entry and the next symbol. This scheme paved the way for LZW (Lempel-Ziv-Welch), a widely used variant that employs a growing dictionary and has been adopted in formats such as GIF. The development of LZW and related variants influenced the deployment of compression technology and patent activity in the 1980s and 1990s.

Impact and usage: The Lempel-Ziv family is foundational in data compression. Modern compressors often combine LZ77-style matching with entropy coding, while LZ78-derived approaches remain relevant for specific data types. The algorithms are valued for their simplicity, speed, and ability to compress data with redundancy without requiring prior knowledge of the source.