The present invention is intended to provide an image processor that can reduce color unevenness occurring in a composite color image formed by overlapping different types of inks due to a variation in printing characteristic among a plurality of nozzles while suppressing a reduction in processing speed in generation of printing data. The image processor converts a color signal indicating the image represented by a plurality of elements to a color signal corresponding to the plurality of inks with use of a conversion table determined on the basis of ejection characteristics of nozzle groups corresponding to the plurality of inks so as to suppress color unevenness occurring in a composite color image due to a variation in ejection characteristic among the plurality of nozzles.