1. An image processing apparatus for generating print data used in each of K relative scans performed on a unit area on a print medium by a print head for discharging ink, the print data determining discharge or non-discharge of ink to each pixel area corresponding to a plurality of pixels in the unit area, the image processing apparatus comprising: one or more processors; and one or more computer-readable media coupled to the one or more processors, the one or more computer-readable media storing instructions that, when executed by the one or more processors, cause an image processing device to perform operations comprising: a first acquiring step to acquire image data that corresponds to an image to be printed in the unit area and that determines an attribute of each of the plurality of pixels in the image, and a number of discharges of ink from zero to N (N≥2) to each of the plurality of pixels; and a generating step to generate the print data based on the image data acquired by the first acquiring step, and K mask patterns that correspond to the K scans and that determine allowing or disallowing ink to be discharged in accordance with the attribute and number of discharges indicated at each of the plurality of pixels by the image data, wherein first print permitting pixels and second print permitting pixels are placed in the K mask patterns such that (i) a difference between a number of the first print permitting pixels placed in J (1<J <K) mask patterns corresponding to J scans from the first scan to the J-th scan among the K scans and the number of the first print permitting pixels placed in K−J mask pattern corresponding to K−J scans from the J +1-th scan to a K-th scan among the K scans is a first value, and (ii) a difference between a number of the second print permitting pixels placed in the J mask patterns corresponding to the J scans and the number of the second print permitting pixels placed in the K−J mask patterns corresponding to the K−J scans is a second value larger than the first value, the first print permitting pixels allowing ink to be discharged when the attribute is a first attribute and the number of discharges is M (1≤M≤N), the attribute and number of discharges being indicated by the image data, and disallowing ink to be discharged when the attribute is the first attribute and the number of discharges is M−1 , the attribute and number of discharges being indicated by the image data, the second print permitting pixels allowing ink to be discharged when the attribute is a second attribute different from the first attribute and the number of discharges is M, the attribute and number of discharges being indicated by the image data, and disallowing ink to be discharged when the attribute is the second attribute and the number of discharges is M−1 , the attribute and number of discharges being indicated by the image data, and wherein the print head is able to discharge an ink of a first color and an ink of a second color different from the first color, the first acquiring step acquires first image data corresponding to the first color ink, and second image data corresponding to the second color ink, and the generating step (i) generates the print data corresponding to the first color ink used in the K scans based on the first image data acquired by the first acquiring step and first K mask patterns corresponding to the first color ink, and (ii) generates the print data corresponding to the second color ink used in the K scans based on the second image data acquired by the first acquiring step, and second K mask patterns corresponding to the second color ink.