When an image processing apparatus of one aspect of this invention corrects input image data using correction values (misregistration correction amounts Δy), it determines whether or not image data to be corrected using amounts Δy includes a specific pattern which may cause density unevenness in an image to be formed. When the image processing apparatus determines that the image data includes the specific pattern, it modifies amounts Δy corresponding to pixels including the specific pattern of the amounts Δy using any of a plurality of different predetermined modulation amounts (modification values). Furthermore, the image processing apparatus corrects the image data for respective pixels using either the amounts Δy before modification, or the modified amounts Δy when the modification is done.