An image processing method includes the steps of converting input image data to ink color data corresponding to each amount of a plurality of colors of achromatic inks used for printing, and generating printing data for first, second and third achromatic inks based on the ink color data. The printing data is used for printing by causing a printing head to scan a common image area in a printing medium a plurality of times, the printing head ejecting the plurality of colors of inks. The converting step converts the input image data to ink color data for the first, second and third achromatic inks so that the first achromatic ink is used with respect to a value of the input image data indicating achromatic color, and the generating step generates the printing data for the first, second and third achromatic inks so as to (a) make a printing duty for the first achromatic ink during first half of the plurality of scans higher than a printing duty for the first achromatic ink during the latter half of the plurality of scans, and (b) make printing duties for the second and third achromatic inks during the latter half of the scans higher than in the first half of the scans.