An image processor for a printing apparatus which performs printing by using a first nozzle array corresponding to a first color ink and a second nozzle array corresponding to a second color ink different from the first color ink: the first nozzle array and the second nozzle array being spaced in a direction perpendicular to a nozzle arrangement direction of the arrays of nozzles, the image processor comprising: a storage means configured to store a plurality of conversion tables, each conversion table relating to one of a plurality of nozzle groups for printing a unit area, which unit areas are made by dividing a printable area of a printing medium in the nozzle arrangement direction, each of the plurality of nozzle groups is composed of at least one nozzle of the first nozzle array and at least one nozzle of the second nozzle array; a conversion means configured to convert each of pieces of the image data corresponding to the respective unit areas of the printing medium using a corresponding one of the plurality of conversion tables that are three dimension look-up-tables for converting color image data into converted color image data; an ink conversion processor configured to convert the converted color image data into ink color signal image data; and a head-shading processor configured to subsequently correct the ink color signal image data using a one dimensional lookup table according to ejecting volumes of the nozzles of the print heads such that the number of dots printed is varied depending on each nozzle to provide a substantially even density among nozzles; wherein: the plurality of conversion tables are configured to reduce a color difference among the plurality of unit areas, caused by variation of ejecting characteristics of nozzles of the first nozzle array and variation of ejecting characteristics of nozzles of the second nozzle array, when an image of predetermined color that is made by at least the first color ink and the second color ink is printed. a storage means configured to store a plurality of conversion tables, each conversion table relating to one of a plurality of nozzle groups for printing a unit area, which unit areas are made by dividing a printable area of a printing medium in the nozzle arrangement direction, each of the plurality of nozzle groups is composed of at least one nozzle of the first nozzle array and at least one nozzle of the second nozzle array; a conversion means configured to convert each of pieces of the image data corresponding to the respective unit areas of the printing medium using a corresponding one of the plurality of conversion tables that are three dimension look-up-tables for converting color image data into converted color image data; an ink conversion processor configured to convert the converted color image data into ink color signal image data; and a head-shading processor configured to subsequently correct the ink color signal image data using a one dimensional lookup table according to ejecting volumes of the nozzles of the print heads such that the number of dots printed is varied depending on each nozzle to provide a substantially even density among nozzles; wherein: the plurality of conversion tables are configured to reduce a color difference among the plurality of unit areas, caused by variation of ejecting characteristics of nozzles of the first nozzle array and variation of ejecting characteristics of nozzles of the second nozzle array, when an image of predetermined color that is made by at least the first color ink and the second color ink is printed.