If pixel segment insertion/extraction control by random number control which is uniform irrespective of a type of image data is performed, in the case of a character or diagram, main scanning positions where the pixel-segment insertion/extraction is executed become discontinuous in a sub-scanning direction, and image quality deteriorates. To solve the above problem, there is provided an image forming apparatus having: a unit for dividing an image into a plurality of areas in the main scanning direction; a unit for setting a reference area for performing pixel segment insertion/extraction control in each of divided areas; and a unit for deciding a position where the pixel segment insertion/extraction control in each of the divided area, in accordance with attribute information of image data in the set reference area.