A unit acquires first image data expressing a color of an image and second image data expressing a feature of the image. A unit color-separates the first image data into first and second color material amount data. A unit generates inverted data by inverting the second image data. A unit generates first corrected data from the first color material amount data and the inverted data and generates second corrected data from the second color material amount data and the second image data. A unit generates, based on the first corrected data, first data indicating on dot printing positions during a printing and scanning operation, generates, based on the second corrected data, second data indicating on dot printing positions in the operation, and generates, based on the first and second data, image forming data.