1. An image processing apparatus comprising: a first image reading unit configured to acquire monochrome image data by reading an image in monochrome from an original document; a second image reading unit configured to acquire color image data by reading an image in color from an original document; an extraction image generation unit configured to generate image data by extracting a chromatic image region in the color image data read by the second image reading unit; and a luminance correction unit configured to make a correction to increase, based on the image data generated by the extraction image generation unit, luminance of a monochrome signal which is included in the monochrome image data read by the first image reading unit and corresponds to the chromatic image region extracted by the extraction image generation unit.