Lempel-Ziv Compression. All three varieties are included — LZ77, LZ78, and LZW.

This AV is designed to allow the student to trace and explore the behavior of the LZ77, LZ78, and LZW compression algorithms on small example data sets in which the alphabet comprising the text to be compressed is purposely limited to allow the student to focus on the specific actions of the algorithm. As such it is not designed to illustrate how the algorithm performs on large-volume data sets. Within that constraint, it achieves its purpose very well. The student can walk through each of the algorithms step-by-step or let them run to completion to "see the final answer" immediately. Accompanying pseudocode is displayed. The visualization can't easily return to a previous step, so it is awkward when one becomes lost in interacting with a visualization because one must re-start the visualization from the beginning.

This AV is packaged as an application in a jar file that you obtain at the above URL.   Once you have downloaded the LZ.jar file, run it from your command line by: java -jar LZ.jar  Or your OS may be jar-file-aware and allow you to run it by double-clicking.

The algorithms used in this AV follow closely the description of the algorithms in "Introduction to Data Compression" by Sayood (Morgan Kaufmann). As such this AV is most effective when used to supplement a presentation of LZ compression that is integrated with that book. The AV comes with canned examples taken from that book, and also allows the student to input their own examples for more exploration. Students may therefore view this AV as providing an infinite reservoir of examples upon which they can practice until they master the basic steps of each of these non-trivial algorithms.