Incremental frequency count - a post BWT-stage for the Burrows-Wheeler compression algorithm

The stage after the Burrows-Wheeler Transform (BWT) has a key function inside the Burrows-Wheeler compression algorithm as it transforms the BWT output from a local context into a global context. This paper presents the Incremental Frequency Count stage, a post-BWT stage. The new stage is paired with a run length encoding stage between the BWT and entropy coding stage of the algorithm. It offers high throughput similar to a Move To Front stage, and at the same time good compression rates like the strong but slow Weighted Frequency Count stage. The properties of the Incremental Frequency Count stage are compared to the Move To Front and Weighted Frequency Count stages by their compression rates and speeds on the Calgary and large Canterbury corpora.