1. An image forming apparatus comprising: an obtaining unit that obtains image data; an identification unit that identifies a fine line part in the image data; a correction unit that corrects a density value of the fine line part and a density value of a non-fine line part adjacent to the fine line part; an exposure unit that exposes a photosensitive member based on the image data in which the density values of the fine line part and the non-fine line part have been corrected, wherein an exposure spot corresponding to the fine line part and an exposure spot corresponding to the non-fine line part are overlapped with each other, and a combined potential is formed on the photosensitive member by the exposure spot corresponding to the fine line part and the exposure spot corresponding to the non-fine line part; and an image forming unit that forms an image on the exposed photosensitive member by developing agent adhering on the exposed photosensitive member according to a potential on the exposed photosensitive member formed by the exposure unit, wherein the correction causes a peak of the formed combined potential to reach a target potential and a size of a part of the formed combined potential whose potential is greater than a predetermined potential to reach a target size.