Data compression and decompression method and apparatus with embedded filtering of infrequently encountered strings

摘要

A data compression and decompression system based on the LZW data compression and decompression methodology that includes exclusion tables storing strings that are infrequently encountered. If an extended string formed for updating the compressor and decompressor dictionaries is included in the exclusion tables, the extended string is not stored and the code counter for assigning codes to dictionary strings is not advanced. In this manner, dictionary codes are not usurped by infrequently encountered strings.