1. An image processing apparatus that generates print data used for performing printing by using a printing head provided with a plurality of nozzle arrays that eject inks of different colors, based on image data, said apparatus comprising: a correcting unit configured to correct a value of the image data on the basis of correction parameter; and a selecting unit configured to, from a memory retaining the correction parameters to be made correspond to respective combinations of printing characteristic ranks of nozzles with respect to inks of different colors, select the correction parameter of the same combination of printing characteristic ranks as a combination of printing characteristic ranks that is obtained correspondingly to respective one or plurality of nozzles for ejecting inks of different colors to a same area of a printing medium, wherein said correcting unit corrects the value of image data on the basis of the correction parameter that is selected by said selecting unit correspondingly to the respective one or plurality of nozzles.