1. An image compression method comprising the steps of: (a) setting a plurality of representing patterns and a plurality of binarized block patterns, each of said binarized block patterns comprising a plurality of bits and a number of said representing patterns being less than a number of said binarized block patterns, each of said representing patterns having a specific relationship with at least one of said plurality of binarized block patterns; (b) dividing an image with multiple gradations into a plurality of pixel blocks, each of said pixel blocks comprising a plurality of pixels; (c) binarizing pixel levels of said pixels in each of said pixel blocks to encode said pixel blocks to one of said plurality of binarized block patterns; and (d) replacing said one of said plurality of binarized block patterns with one of said representing patterns which has said specific relationship with said one of said plurality of binarized block patterns; wherein step (d) comprises inverting polarities of a predetermined number of bits of said one of said plurality of binarized block patterns to replace said one of said plurality of binarized block patterns with said one of said representing patterns.