1. An image processing apparatus comprising: a character data extraction unit extracting character data, forming a character image serving as a target to be read by an image reading apparatus, from image data; an outline data generation unit generating outline data forming an outline image of the character image from the character data; and an image density changing unit changing an original image density of the outline image to a lower but greater than zero density based on the outline data generated by the outline data generation unit, wherein the outline data is an outside portion of a character image, and is region data having a prescribed width adjacent to the character image.