1. A printing control method of generating print data to be supplied to a print unit to print, the print unit forming dots on a print medium by ejecting ink droplets of at least one type of colored ink containing a color material and a quality-enhancing ink for enhancing quality of a printed material, the printing control method comprising: (a) a color conversion step of converting pixel values representing a color in each pixel of the image data into multi-tone data of each ink, the multi-tone data of each ink being for expressing the color with the at least one colored ink and the quality-enhancing ink available in the print unit; and (b) a tone-decreasing step of generating dot data representing a dot formation state of a colored dot formed with the at least one colored ink and a transparent dot formed with the quality-enhancing ink in each pixel, according to the multi-tone data of the each ink generated by the color conversion, wherein the tone-decreasing step includes the step of generating transparent dot data by a process configured such that size of first processing-targeted pixels is larger than size of second processing-targeted pixels, the first processing-targeted pixels being targeted for processing in the transparent dot data generating process, the second processing-targeted pixels being targeted for processing in the colored dot data generating process, and wherein the first processing-targeted pixels correspond to groupings of the second processing-targeted pixels, and pixel values of the first processing-targeted pixels are determined according to pixel values of the second processing-targeted pixels belonging to the first processing-targeted pixels.