1. An optical reader for decoding an encoded candidate character of a symbology, the optical reader comprising: a lens system for focusing an illuminated encoded candidate character at a plane of focus; an optical sensor having as an input the detected light intensity corresponding to the illumination reflected from the encoded candidate character, and having as an output an electrical signal encoding information representative of the encoded candidate character; wherein the optical reader accesses a distance map comprising a seed codeword and a plurality of seed distance values, each seed distance value comprising a computed distance from the seed codeword to a character of the symbology; wherein the optical reader computes a candidate distance value from the seed codeword to the encoded candidate character; wherein the optical reader compares the encoded candidate character to a subset of the characters of the symbology, the subset comprising characters of the symbology having seed distance values within a specified range of the candidate distance value.