Hierarchical coding of line - Drawing data described by the chain - Code sequence

A hierarchical encoding scheme has been proposed to realize efficient coding of line-drawing data described by the chain-code sequence. For links, each of which is an ordered pair of succeeding grid points in the sequence, the encoding scheme builds up a pyramid-like code structure by uniting links by twos, and it has the following advantages: 1) line drawing can be decoded in various scales (power of 2s); 2) high coding efficiency is obtained for each layer; and 3) degradation in display quality due to a blot-like effect in small-scale layers is relaxed. Concerning the coding efficiency in item 2), an experiment using coastline data obtained from a topographical map gave the coding rate for each layer of about 1. 1 bits/link. This shows that the proposed scheme is more efficient than data filing by independent encoding of each scale data.