1. An imaging system comprising: an imaging unit for producing an image within a given field of view; an image defect detector for detecting a defective area from a first image that is produced by the imaging unit without a subject in the given field of view; a size enlarging unit for forming a deemed defective area having an enlarged size consisting of pixels of the first image corresponding to a defective area detected by the image defect detector and at least one of pixels adjacent to these pixels; and an image defect correcting unit for correcting a second image produced by the imaging unit with a subject located within the given view of field according to a deemed defective area formed by the size enlarging unit.