Multi-channel signal processing in an optical reader

摘要

An optical reader, for example a field of view reader or a flying spot scanner for reading a printed indicia such as a bar code symbol includes a light source and a light detector, and at least two channels associated with the detector for carrying signals corresponding to light detected by the detector at different resolution levels, thus simplifying the decoupling of signals allowing a single reader to be used regardless of the resolution level of the indicia to be read. In order to arrive at an improved signal to noise ratio of a bar code symbol being read, a processor produces two signals at respective first and second channels, the signal in the second channel being buffered and merged with a later signal in the first channel allowing time averaging out of the noise portion of the signal and enhancement of the information portion of the signal. An improved system for detecting defects in a printed bar code symbol includes processing means for comparing the width of a detected space with the width of neighbouring spaces and identifying the space as a defect if its width is less than a predetermined proportion of the width of neighbouring spaces.