Bar code symbol readers with edge enhancement.

摘要

The depth of modulation of an analog electrical signal generated by a photodetector during scanning of a bar code symbol in the field of bar code scanning is enhanced under circumstances where the modulation of the analog signal has been degraded, for example, by an oversized sampling aperture in relation to the widths of the symbol elements. The anaiog signal has high frequency components whose low amplitudes are increased in magnitude prior to being conducted to a digitizer. The effect of noise introduced during reading of the bar code is cancelled by comparing in the comparator, the modulation-enhanced analog signal with the second derivative signal derived from the modulation-degraded unenhanced analog signai. The output of the comparator is a digital output signai having a logical levei dependent on the amplitude of the enhanced analog signai at each zero crossing of the second derivative signal. The digital output signal is a closer representation of the code read by the scanner.