Patent ID: 6382511
Filing Date: 2002-05-07
Classification: G06K

Abstract:
A barcode processing system for processing a photosignal produced by a photodetector in response to light reflected from a barcode, the barcode comprising elements including wide and narrow bars and spaces, onto the photodetector, the system comprising:a differentiator for producing a first derivative signal based on the photosignal; an analog to digital converter for producing a digital first derivative signal based on the first derivative signal, the digital first derivative signal comprising a series of samples taken at equal intervals in order to create an accurate representation of the first derivative signal, the intervals being independent of the characteristics of the first derivative signal; and a processor for processing the digital first derivative signal to recognize logic transitions represented by the photosignal, the processor being operative to differentiate the first derivative signal to produce a second derivative signal, the processor also being operative to create a threshold based on peaks of the photosignal, the processor being further operative to recognize a logic transition when the second derivative signal experiences a zero crossing within a predetermined time window after an amplitude peak of the digital first derivative signal exceeds said threshold, said threshold comprising an AC threshold component added to a DC threshold component, said AC threshold component based on amplitudes of peaks of said digital first derivative signal.