Encoding of line drawings with multiple hexagonal grid chain code

Abstract

AbstractThis paper discusses the encoding of line drawings using a hexagonal quantization grid. When an efficient encoding of line drawings is required in general, one must seek the encoding method which minimizes the code assigned to the unit length of the line‐drawing, under the constraint for the quantization error. The multiple square grid chain code, which was already proposed, is one such encoding method. This paper describes the result of a study on the multiple hexagonal quantization grid, which is more efficient than the former method. In those methods, the quantization grid is not fixed. The quantization points are arranged on the edge of the grid, and the quantization is made more efficient by adjusting the point of quantization grid connections according to the previous situation of quantization. The rate‐distortion value of the multiple hexagonal grid chain code is shown to be approximately 0.7 times that of the multiple square grid chain code and approximately 0.45 times that of Freeman's chain code. The reason for the differences are discussed in some detail, and the actual algorithm and the processing time are described, considering the real‐time property of the code.