US Patent 7961355 Generation of dither matrix

A printing method includes: providing a print head that includes a plurality of nozzle arrays for ejecting at least 3 colors of inks; performing a halftone process with a dither matrix on image data to generate dot data that represents a state of dot formation at each pixel. The dither matrix includes a single reference matrix that is set by determining threshold values in the reference matrix based on a predetermined index value being calculated based on an arrangement pattern of at least two colors of dot groups among M colors (M is an integer of at least 3 and less or equal to N) of dot groups among the at least N colors of dot groups, with respect to at least some tone values among the input tone values.