1. A density correction value calculation method for a printing device comprising: a first nozzle column in which first nozzles for ejecting ink are aligned in a predetermined direction; a second nozzle column in which second nozzles for ejecting the ink are aligned in the predetermined direction, the second nozzle column being disposed to form an overlapping region in which an end on one side in the predetermined direction overlaps an end on the other side in the predetermined direction of the first nozzle column; and a movement part for relatively moving a medium in an intersecting direction that intersects the predetermined direction; wherein the printing device ejects the ink in the overlapping region with a total duty divided between the first nozzles and the second nozzles; the correction value calculation method comprising the steps of: (A) determining the density of each pixel column composed of pixels aligned in the intersecting direction in a duty determination pattern, and also determining the density of each pixel column in the duty determination pattern in which a plurality of overlapping region patterns are formed with a total duty higher than the highest duty of non-overlapping regions which are not the overlapping regions; (B) specifying the total duty for which the lowest density of the pixel column densities of the overlapping regions is equal to or greater than the lowest density in the pixel columns of the non-overlapping regions; and (C) calculating a density correction value of the pixel columns using a density correction pattern formed with the specified total duty, and also calculating a density correction value so that the lowest density of the pixel column densities of the density correction pattern is a reference.