1. A printing method of printing on a printing medium, comprising: generating dot data representing a status of dot formation on each of print pixels of a print image to be formed on the print medium, by performing a halftone process on image data representing a input tone value of each of pixels constituting an original image; providing a print head having a plurality of nozzle groups that eject inks of mutually different colors; and generating the print image by mutually combining dot groups of multiple colors formed in at least one scan in a common print area, by forming each dot group with each of the plurality of nozzle groups during each scan of the print head in response to the dot data, each of the dot groups being mutually different in color, wherein the generating of the dot data includes setting a condition for the halftone process for reducing contact between the dot groups of the at least two specific colors within at least part of tone values, for at least two specific colors of dot groups among the dot groups of multiple colors, the generating of the print image includes generating the print image by mutually combining dot groups of multiple colors formed in each of a plurality of scans in a common print area, and the at least two specific colors of dot groups include a plurality of dot groups of multiple colors formed in a same scan, and a plurality of dot groups of a same color formed by consecutive scans.