Method and apparatus for pattern noise correction

Abstract

Fixed pattern noise manifested as percentage variations between the apparent sensitivities of sensor elements in a solid state image sensing array is reduced by removing one or more percentage portions of charge from a charge packet generated by an element of the sensing array. In a preferred embodiment, a percentage portion of charge is removed by dumping the portion of charge appearing under one part of a split electrode in a charge coupled device (CCD) shift register. A programmed memory controls the operation of the split electrode CCD device to provide the required corrections. To program the memory, the output of the image sensing array is measured with a non-image-wise input; and a particular charge packet size (e.g. the smallest useable charge packet produced by the array) is chosen as a reference. The percentage corrections required to adjust the relative sizes of the other charge packets from the array to make them equal in size to the reference charge packet are calculated and converted to corresponding control signals for the split electrode CCD device. The control signals are then stored in the memory. During subsequent operation of the image sensing array, the size of a charge packet is adjusted in the split electrode CCD shift register, under control of the control signals stored in the memory, to remove fixed pattern noise.