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: a first acquisition unit configured 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 generation unit configured to generate the print data based on the image data acquired by the first acquisition unit, 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.