Abstract: Printed bar codes which are either biphase modulated or bar-no-bar modulated are read as they pass an optical sensor. The video signal generated thereby is given a waveform having a constant reference level within an amplitude envelope of constant magnitude. The signal then is differentiated to provide a bipolar waveform having character dependent properties. The bipolar waveform is applied to a synchronizer to establish a digital synchronization waveform defining the time periods during which bar signals may occur. The bipolar waveform also is separated into positive and negative halves which are integrated separately and compared to a predetermined threshold to detect the presence of a bar. When a bar is present, the time of occurrence of the bar signal peak is correlated with the synchronization signal to identify either a logic one or a logic zero representation from the half-period position of the bar signal.