To suppress streaky image gradation unevenness that occurs in an image, as compared with when a substitution rate of chromatic color dots and light black ink color dots for recording an image is uniform.
A block with no second color conversion applied thereto is selected (step 200) and a pixel with no second color conversion applied thereto and included in the selected block is selected (step 202). A minimum one of gradation values of respective colors Y, M, C, of the selected pixel is selected as a substitution reference value (step 204), the substitution reference value is multiplied by an element of a substitution rate matrix corresponding to the selected pixel, as a replacement value (step 206). The gradation values of the respective colors Y, M, C are decreased only by the substitution value operated in step 206 (step 208) and a gradation value of a color K is increased only by the substitution value (step 210).
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Kato Kazunori
Katsuichi Nishimoto
Hiroshi Fukuda