Optical reader head with video compensation method and circuit which integrates four adjacent pixels into a composite pixel

摘要

An optical reader head with a video compensation circuit for use in high speed document reading. The reader head utilizes small focussed bulbs to illuminate the scanning line, with the head being comprised of first and second body sections housing a lens which focusses the light reflected from a document at the scanning line to a light array comprised of 256 sensors. Light from four adjacent sensors along the scanning line is integrated to produce a composite pixel which becomes one of 64 such composite pixels for a scanning line of data permitting the use of low wattage bulbs and also eliminating the possibility of burning a jammed document. A peak comparison PROM is used for adjusting document background levels, for example, for use in thresholding the pixel data. The peak comparison PROM is used as a 14 bit address table with six bits being used for the gray level signal of the incoming composite signal, with three bits being used for a "Mode Value", and with five bits being used for a "Peak Gray Scale Value" from a prior scan. A special test circuit is used to insure accurate focussing of the lens.