Multi-valued image data is separated into data in units of nozzle groups of the individual colors of a printhead, and each divided multi-valued image data is converted into n-valued image data consisting of a plurality of bits. Based on the n-valued image data of the corresponding colors, print codes are generated and are transmitted to a printer apparatus. The printer apparatus receives the print codes, stores them in print buffers of the corresponding colors, and generates print data based on the print codes using mask patterns set in correspondence with image data of the individual colors. The print timing in each scan of the printhead is determined in accordance with the significant bit position in the print data, and an image is printed on the basis of the print data by multi-pass printing.