A printing apparatus can reduce degradation in print quality of a printed image, notably in a highlight portion or an intermediate gradation portion, in the case where the image is printed by forming dots of a plurality of sizes. Specifically, data causing larger and smaller cyan ink droplets, respectively, to be ejected is independently subjected to a conversion to n-value process. Thus, the data for larger ink droplets is present in a portion of printing data which corresponds to the highlight portion or intermediate gradation portion of the image. During printing, larger dots are formed in this area, thereby making it difficult to perceive possible stripes caused by the offset of the positions at which smaller droplets impact a sheet.