1. An image forming apparatus comprising: an obtaining unit configured to obtain image data; a specification unit configured to specify a fine line part in the image data; a correction unit configured to correct a density value of the fine line part and a density value of a non-fine line part adjacent to the fine line part such that a combined potential formed on a photosensitive member by an exposure spot with respect to the fine line part and an exposure spot with respect to the non-fine line part becomes a predetermined combined potential; an exposure unit configured to expose the photosensitive member based on the image data in which the density values of the fine line part and the non-fine line part has been corrected, wherein the exposure spot with respect to the fine line part and the exposure spot with respect to the non-fine line part are overlapped with each other; and an image forming unit configured to form 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.