1. An image processing apparatus comprising: an image obtaining portion configured to obtain a first image and a second image that have exposures different from each other; a region selecting portion configured to select a first region that is different from a region containing a luminance saturation part from the first image, and select a second region that corresponds to the region containing the luminance saturation part of the first image from the second image; an image restoration processing portion configured to perform an image restoration processing so as to reduce an aberration by using an image restoration filter generated based on an optical transfer function for the first region of the first image and the second region of the second image; and an image replacing portion configured to replace the region containing the luminance saturation part of the first image with the second region of the second image so as to synthesize the first region of the first image and the second region of the second image to generate one image, wherein the image restoration filter is generated based on the optical transfer function of an image pickup optical system which is used for taking the first image and the second image.