1. An optical character recognition page reader for reading documents containing characters and for producing an output identifying the characters read, comprising: means for receiving and illuminating at least one document to be read; an array of light-sensitive elements for converting variations in light patterns on the document due to the characters into variations in an electrical output signal; a lens positioned between the document and the array for focusing an image of a portion of a document onto the array; lens moving means for moving the lens so that all portions of the document are sequentially focused on the array; and an electronic control circuit for recognizing the variations in the outputs of the light sensitive elements as the characters being read on the document and for producing digital outputs in response thereto, said control circuit comprising: means for transferring the present outputs of elements in parallel to a shift register; means for storing previous maximum white reference signals for each element of the array; reference comparator means for comparing the present output of each element of the array delivered in series from the shift register to the pertaining previously stored maximum white reference signal delivered in series from the means for storing, said comparator means producing an output whenever the present output of the element is larger than the pertaining previously stored maximum white reference signal; and means for incrementally increasing the value of the previously stored maximum white reference signal whenever the reference comparator means has an output.