Weighted Burrows–Wheeler Compression

Abstract

A weight-based dynamic compression method has recently been proposed, which is especially suitable for the encoding of files with locally skewed distributions. Its main idea is to assign larger weights to closer to be encoded symbols by means of an increasing weight function, rather than considering each position in the text evenly. A well known transformation that tends to convert input files into files with a more skewed distribution is the Burrows–Wheeler Transform (BWT). This paper proposes to apply the weighted approach on Burrows–Wheeler transformed files. While it is shown that the compression performance is not altered for static and adaptive arithmetic coding by any permutation of the symbols, hence in particular for BWT, empirical evidence of the efficiency of the combination of BWT with the weighted approach is provided.