An image forming apparatus includes plural image forming units of plural colors, each including a print head including plural LED chips aligned in a main scanning direction; a screen angle selecting unit that selects screen angles for the plural colors respectively based on the amounts of skew of the plural image forming units; an image processing unit that performs image processing on input data to be expressed by pixels of the plural colors such that the pixels of the colors have the corresponding screen angles selected by the screen angle selecting unit; a correction amount determining unit that determines a total amount of skew correction based on the amount of skew detected by the skew detection unit, and determines the amounts of skew correction in the sub-scanning direction for predetermined groups of the pixels, based on the total amount of skew correction, for each of the colors.