Two-dimensional dot codes for product identification

In automated manufacturing the two-dimensional representation of product identification numbers by means of square dot codes offers a number of advantages over the use of bar codes. In this paper a method is described for the encoding of product identification numbers into square matrices of round dots on a contrasting background. It consists of an optimal source coding scheme for the encoding of identification numbers into channel message words, and a channel coding scheme offering error-detection and error-correction for random bit errors (dot corruptions). For the channel coding scheme, a special class of error-correcting codes is introduced, called {\em square-cyclic codes.} It is shown how to transform quasi-cyclic and (shortened) cyclic codes into square-cyclic codes.