A quantization method of line drawings using directional‐difference codes with adaptive line segments

Abstract

AbstractThis paper proposes a highly efficient coding method suited to the storage and transmission of complicated line drawings such as topographical map. Instead of using the method based on the fixed‐length segment such as Freeman's chain code, the segment length is made variable according to the state of the curve. The high efficiency is realized by further adding the directional‐difference code. In the method employing variable‐length segment, there is a danger that the approximate error is increased with the length of the segment. Consequently, a scheme is employed in which the permissible error is specified, and the coding is performed within the error limit. To simplify the encoding procedure, several quantization templates are prepared with different segment lengths, and the approximating segment is selected by taking the template according to the state of the curve. Avoiding the increase of coding complexity by adding the template discrimination code, the template to be used is selected based on the code sequence generated in the past. By this scheme, although depending on the complexity of the line drawing, the coding complexity can be reduced by 25 to 40 percent considering only the effect of variable segment length.