An image forming apparatus forms an image by optical scanning. The image forming apparatus includes: a light source; an image processing unit that processes image data; a modulation signal generation unit that generates a light source modulation signal; a light source drive unit that drives the light source based on the light source modulation signal; and a correction value identifying unit that identifies a correction value for correcting a registration error of an image to be formed. The image processing unit performs first image processing of image data with first resolution based on a correction value identified by the correction value identifying unit, the first image processing including deformation processing and gradation processing of the image data. The modulation signal generation unit converts image data processed in the image processing unit into image data with resolution higher than the first resolution and performs second image processing.