Lossless image compression has often employed techniques quite separat
e from those used for text compression or lossy image compression; mos
t standards today employ modelling followed by coding (e.g. the JBIG s
tandard, the IBM Q-coder, CCITT Group 4). Constantinescu and Storer pr
esent a lossy image compression scheme that can be viewed as a general
ization of lossless dynamic dictionary compression ('LZ2'-type methods
) to two dimensions with approximate matching; recently, Constantinesc
u and Storer have experimented with this approach for lossless hi-leve
l image compression with great success, Here we generalize 'LZ1'-type
methods (that identify matches in previously seen text) to lossless im
age compression. We examine complexity issues and finish by considerin
g practical 2-D implementations for bi-level images.