Method and apparatus for reading and decoding a high density linear bar

Abstract

A method and apparatus for decoding a high density linear bar code of the type of the Universal Product Code (UPC) symbol and derivatives thereof. The method comprehends unambiguously decoding the encoded characters of the symbol by the use of primary ratios representative of the ratios of the sum of the widths of selected coding modules and secondary decoding ratios. The secondary ratios are selected in the event of any out-of-tolerance printing of the symbol for permitting the secondary ratios to be utilized with the primary ratios for resolving any possible ambiguities. The method and apparatus is applicable to scanning the UPC symbol by means of a hand-held wand as well as laser beam scanning. The apparatus contemplates the measuring of the widths of the coding modules and storing the width measurements in a memory without decoding. Since the symbol includes a standard pattern having known module-to-module width ratios, this information is utilized for processing the stored data to locate the measurement data in the memory, compute the printing tolerance character and then compute the desired ratios for decoding the scanned symbol.