1. A method of processing image signals derived from a device by a scanning electron microscope, said method comprising the steps of: initially scanning a reference specimen by the scanning electron microscope for a plurality of scans to provide reference image data; determining an evaluated relative feature function of an electro-optical cylinder of the scanning electron microscope based upon the reference image data obtained from the plurality of scans of the reference specimen by the scanning electron microscope; scanning the specimen to be inspected by the scanning electron microscope under the same conditions in effect for the scanning of the reference specimen, but for a plurality of scans smaller in number than the plurality of scans of the reference specimen by the scanning electron microscope in obtaining the reference image data for providing specimen image data; and correcting the specimen image data in accordance with the evaluated relative feature function of the electro-optical cylinder based upon the reference image data.