Circuit arrangement for white level acquisition for the black/white

Abstract

A circuit arrangement is composed of a first adder whose first output is assigned to the digitized output signals of the photosensors and a second input connected to the outputs of a white level memory, and a second adder at whose input side the currently stored white level are linked with the correction signal and which reads the resultant signal back into the white level memory, the comparator following the first adder which, dependent upon the threshold level derived from maximum and average blackening values of the output signal of the first adder supplies a black signal or a white signal. A correction signal derived from a plurality of influencing variables serves for white level correction, the correction signal supplying a white level increment/decrement for delivery into the white level memory dependent on a carry signal that appears or, respectively, that does not appear at the first adder.