Dc restoration of sampled imagery signals

Abstract

The problem of error-introducing artifacts associated with the sampling of the pixels of a solid state imager is obviated by controllably clocking the A-D converter to which the sampled pixel signals are applied, such that the A-D converter digitizes successive pixel samples only during those times that are exclusive of those times when switching transitions occur during the sampling of the imager pixels. The D.C. restoration level is established in accordance with the contents of `dark ` pixel samples, which are exclusive of the switching transitions. In one embodiment, the selective D.C. restoration process is accomplished by coupling the output of the A-D converter to a digital-to-analog (D-A) converter. The D-A converter is clocked during the times that the A-D converter digitizes dark samples, so that it generates successive dark sample-representative voltages. Difference between these analog voltage values and a prescribed level are integrated and fed back to the input to the (A-D) converter as a D.C. restoration offset. In a second embodiment of the invention, the difference between the output of the analog-to-digital converter and a prescribed digital code is used to control the operation of a digital counter. The D.C. reference level is established in accordance with the contents of the digital counter.