Coding efficiency of multi-ring and single-ring differential chain coding for telewriting application

The availability of small personal digital assistants (PDAs) with a touchscreen and communication capabilities has been an influential factor in the renewed interest in telewriting, a technique for the exchange of handwritten information through telecommunications means. In this context, differential chain coding algorithms for compression of the handwritten ink are revisited. In particular, it is shown that the coding efficiency of multi-ring differential chain coding (MRDCC) is not always better when compared to single ring differential chain coding (DCC), as previously suggested. These algorithms were tested on over 300 handwritten messages using a relative compactness criterion and a per-length distortion measure. The probabilities of relative vectors in MRDCC and DCC are related, an expression for relative compactness in the MRDCC case is introduced, and the application of Freeman´s (1974) criteria for the selection of the appropriate code for a family of curves is illustrated