Dictionary coder

Dictionary compression, and string replacement method or substitution compression, means all data compression methods which search the raw data for recurring strings to assigned in a so-called dictionary outsource this a substitute symbol and the symbol to be replaced (for example, the position in the dictionary ).

Often dictionary methods are combined with other methods that utilize other forms of redundancy. Quite often, the combination with subsequent entropy coding.

Methods

Some dictionary methods use a static dictionary, whose entries are fixed before the coding and are not changed.

More common are methods that start with a blank or a predefined dictionary and build this during encoding according to the content.

Examples

The 1977 and 1978 published by Abraham Lempel and Jacob Ziv LZ77 and LZ78 method and their numerous descendants and variants ( LZW, LZSS, LZMA, LZO, ...) are based on this principle.

Another example is Sequitur.

• Data compression