Breakpoint skeletal representation and compression of document images

Summary form only given. We present a new method for representation and (lossy) compression of bitonal document images. The technique extracts a skeletal medial axis from each object using a true Euclidean distance map of the image and then finds piecewise linear breakpoints in the skeleton to create a breakpoint skeletal representation, b.p.s. The b.p.s. is encoded for each object as a set of triples. The original binary object is reconstructed by first reconstructing the skeleton using linear interpolation between breakpoints and then fractionally dilating each point on the skeleton with the (linearly interpolated) radius, r/sub i/. For noninteger r/sub i/ fractional dilation provides a natural antialiasing in the reconstructed image. Breakpoints can be extracted to preserve fine detail or a more coarse representation by tightening or relaxing the pruning radius respectively. If, in extracting breakpoints, the pruning radius is set to zero, the reconstruction is almost lossless, but the compression is worse.