Universal text preprocessing for data compression

Several preprocessing algorithms for text files are presented which complement each other and which are performed prior to the compression scheme. The algorithms need no external dictionary and are language independent. The compression gain is compared along with the costs of speed for the BWT, PPM, and LZ compression schemes. The average overall compression gain is in the range of 3 to 5 percent for the text files of the Calgary Corpus and between 2 to 9 percent for the text files of the large Canterbury Corpus.