Patent ID: 6874864

Claim:
An ink jet printing apparatus for forming an image on a print medium by using a print head, the print head having a plurality of nozzles for printing a same color, the ink jet printing apparatus comprising: image forming means for performing a plurality of main scans by scanning the print head relative to a same main scan print area of the print medium and for forming the image onto the same main scan print area by using different respective nozzles of the print head in the plurality of main scanning operations, wherein different thinning out mask patterns are used in the plurality of main scanning operations for printing onto the same main scan print area, and thinned out images according to the different thinning out mask patterns are formed onto the same main scan print area by the different respective nozzles during the plurality of main scanning operations; and printing duty determining means for dividing the same main scan print area into a plurality of divided areas in a sub-scan direction different from a main scan direction, and for determining the printing duty of each of the plurality of divided areas, in each of the plurality of main scanning operations, the printing duty being determined by the thinning out mask pattern, wherein the printing duty determining means performs the thinning out process by the thinning out mask pattern such that the printing duty of one of the divided areas and the printing duty of a second one of the divided areas are different from each other in each of the plurality of the main scanning operations, and the printing duty for the same main scan print area in the main scanning operation in which are used nozzles including an end nozzle of the print head is less than the printing duty for the same main scan print area in another main scanning operation in which the end nozzle of the print head is not used.