1. An image forming apparatus comprising: an applying unit configured to apply a dither matrix to multi-valued image data; and an exposure unit configured to perform an exposure on a photoreceptor drum based on the image data obtained by using the dither matrix applied by the applying unit, wherein the exposure unit is configured to perform additional amount of exposure on the photoreceptor drum in a cycle equal to a cycle of the dither matrix, in addition to an amount of the exposure based on the obtained image data.