1. An image pickup apparatus for picking up an imaging field to produce an image signal, said apparatus comprising: an image pickup device for picking up an imaging field to produce an image signal representative of an image of the imaging field; and a signal processor for processing the image signal; said signal processor increasing, when processing the image signal produced under a predetermined exposure condition, a clamp level for clamping the image signal, performing noise reduction for removing noise of random nature from the image signal prior to correcting a primary black level for the image signal, and then correcting the black level.