Character detection system

Claim 1

In an optical character recognition system having document surface adapted for relative movement with respect to an elongated array of photosensors and having characters formed along a first area of said surface and at least one second area of said surface which contains no character information, means for illuminating said first and second areas of said document surface, and means for imaging a portion of said first and second areas onto said array, a system for the detection of characters on said document surface comprising: an elongated array of photosensors each of like response disposed along an axis angularly disposed with respect to the axis of relative movement and arranged to receive light reflected from said first area of said document surface and operative to provide a plurality of first signals representative of the reflectance of said first area and characters contained thereon; at least one photosensor of like response as said array of photosensors and arranged to receive light reflected from said at least one second area of said document surface and operative to provide at least one second signal representative of the reflectance of said at least one second area; means for amplifying each of said plurality of first signals; means for processing said at least one second signal to provide a reference signal; and a plurality of comparators each receiving said reference signal and a respective one of said amplified first signals and having a threshold level derived from said reference signal, each operative to produce a digital output signal Of one logic level representing character data when the magnitude of said first signal is less than or equal to that of said threshold level, and to produce a digital output signal of another logic level representing the absence of character data when the magnitude of said first signal is greater than that of said threshold level, said means for processing said at least one second signal includes means operative in the absence of said document surface from said illuminating means to clamp said threshold level to a level greater than that of said first signals to cause said comparators to each produce a digital output signal of said one logic level.