An image forming apparatus which performs multicolored printing by overlaying a plurality of printing materials using an electrophotographic process is provided. The apparatus includes a generation unit configured to generate bitmapped data of each of the plurality of printing materials, a detection unit configured to compare bitmapped data of a first printing material and of a second printing material of the plurality of printing materials to detect an overlapping area in which the first and second printing materials overlap, and a control unit configured to decrease the supply amount of the first or second printing material in the overlapping area.