In relation to a superimposed image obtained by superimposing second image data on first image data in which respective pixels are arranged in a staggered pattern, an image forming apparatus discriminates a region where the second image data is superimposed from a region where the second image data is not superimposed. When forming an image in a region determined as the region where the second image data is not superimposed in the superimposed image, the printing mechanism is controlled based on a first control pattern. When forming an image in a region determined as the region where the second image data is superimposed in the superimposed image, the printing mechanism is controlled based on a second control pattern different from the first control pattern.