1. An image forming apparatus comprising: a resolution converting unit configured to convert high-resolution image data into low-resolution image data; an edge judgment unit configured to judge an edge for each region composed of a plurality of pixels in the high-resolution image data; and a density correcting unit configured to make density correction in the low-resolution image data so that the less the number of pixels having a value larger than a threshold value in a region judged as an edge by the edge judgment unit, the larger increase rate of a density in the region of the low-resolution image data corresponding to the region.