An image processor, a printing apparatus, and an image processing method are provided that can reduce, when a plurality of types of inks are used to print an image, the color unevenness that is caused by the variation of ejecting characteristics among a pluralities of nozzles. To realize this, for a color formed by overlapping at least two colors of inks, parameters are prepared that are determined so as to reduce the color difference in the printing medium due to the variation of the ejecting characteristic among the respective pluralities of nozzles. During printing, the parameters are used to correct the first color signal owned by the individual pixels to the second color signal.