Neighboring direction runlength coding: an efficient contour coding scheme

An improved exact coding scheme for a two-tone digital contour is proposed. It is assumed that the contour is one pel thick and perfectly 8-connected. The basic idea of the scheme is to segment the contour at the position where 90 degree bends occur. Each segment is considered as a unit for coding. For coding convenience, the subsegments belonging to the segment, and runs in each subsegment, are identified. The codeword consists of subwords representing the starting direction of the segment, subsegment identification, number of runs in the subsegments, and number of pels in the runs. The scheme has been tested on several contours, and experimental results are presented and compared with those of the best known scheme. It is seen that the proposed scheme is consistently better than the NDSC (neighboring direction segment coding) scheme