Glicbawls is a lossless and/or near-lossless image compression algorithm that apparently does really well on gray-scale images but perhaps not as well on color. This link points to an archived page, as the original has disappeared from the net. As a result, links on the page may or may not work propery

http://web.archive.org/web/20020604145417/http://byron.csse.monash.edu.au/glicbawls/index.
html