An object of this invention is to eliminate graininess caused by superposition of noise on an image reproduced as a hard copy. To achieve this object, this invention provides an image forming apparatus which forms an image corresponding to bitmap image data, including a determination unit which determines from the bitmap image data an image data area where a noise component is superposed, and an image processing unit which performs halftone processing for the bitmap image data so as to decrease the resolution in at least a predetermined direction for the image data area where the noise component is superposed, in comparison with an image data area where no noise component is superposed. More preferably, image formation based on the bitmap image data having undergone halftone processing by the image processing unit is performed by electrophotography, and the image processing unit performs halftone processing by using as the predetermined direction a scanning direction in forming a latent image with a light beam. Alternatively, the image processing unit performs halftone processing by dithering, and uses a threshold matrix having a matrix size larger in at least the predetermined direction for the image data area where the noise component is superposed, in comparison with the image data area where no noise component is superposed.