In image processing, it is possible to suppress density fluctuation and keep graininess low as well as obtain a good balance of the processing load. More specifically, when dividing multi-valued data and generating two-pass multi-pass printing data, divided multi-valued data that is common to the two passes is generated in addition to the divided multi-valued data for each of the two passes. Moreover, quantized data of that common multi-valued data is reflected on the quantized data for each pass. Furthermore, when generating quantized data, a process of generating common data by the aforementioned data division, or a process of performing quantization first without dividing the multi-valued data and then dividing the quantized 2-pass data is selectively performed according to the printing position on printing medium.