US Patent 7193743 Printer driver software product with edge runlength encoder

A printer driver software product includes machine readable instructions for a computer to compress bi-level page description date. The computer, in accordance with the instructions, checks to determine if an edge of a black region in a line of the page is within a predetermined range of pixels from an edge of a black region in a previous line of pixels. If the edge falls within the predetermined range then a symbol is written indicating the presence of the edge and the offset from the referenced edge in the previous line. The end of each line of pixels is determined on the basis of a parameter indicating page width.