An ink-jet printing apparatus printing apparatus prints an image with a plurality of similar color inks having different concentrations and a special ink having a single concentration. In the apparatus, graininess resulting from ink dots is decreased for all hues of the printed image. A decision is made as to whether or not a hue of an image to be printed can be printed with inks without the special ink of a color (for example, special color BL (blue)) having a single concentration. When it is decided that the hue of the image is to be printed with inks without the special color ink, data on ink color BL (blue) is decomposed into data on C (cyan) and data on M (magenta). The hue can be printed without the color BL, thereby significantly decreasing graininess in a portion having this hue.