COMPARING CODING EFFICIENCY OF VECTOR CHAIN CODING AND RUN-LENGTH CODING FOR LINE DRAWINGS

More efficient data compression can be achieved in encoding line drawings by vector chain coding (VCC) than by the traditional runlength coding (RLC), provided the total length of the lines within a line drawing is not excessive. More bandwidth or time can thus be saved in transmitting such pictures by using VCC. Although this has so far been established only intuitively, quantitative analysis and comparison of the coding efficiency of these two codes for line drawings are performed in this paper. The coding efficiency is measured in terms of both per-length coding rate and data compression ratio, which are determined for a class of handwritten line drawings characterised by a proper statistical model. In particular, the critical point of line drawing complexity is derived at which VCC becomes less efficient than RLC. Experimental observations are also presented to verify the theoretical results.