newspaper clippings such as without limitation recycled paper in which the background is not white the output data from section pk is supplied to a device of a next step as read image data ids an image reading operation of an original document in the image reading apparatus includes four steps as illustrated in fig3 that is a standard shading data obtaining mode step 101 an abnormal pixel detection mode steps 102 an uncorrectable pixel column detection mode step 103 and an original document reading mode step 104 in the standard shading data obtaining mode an image of the white plate wt i e standard white image is read before the original document dk is fed the shading correction section sc stores the digital image signal idb which is output by the darkness level correction section bc in the memory wm as standard shading data as illustrated in fig4 the standard shading data falls toward an all black level in continuous pixel regions la and lb which correspond to a size of fouling at a position where fouling adheres at an image reading line in the abnormal pixel detection mode the abnormal pixel detection section is bb examines the standard shading data stored in the memory wm by a commonly known method to detect abnormal pixels the value of the standard shading data of the abnormal pixels is replaced with the.