Image data can be subjected to a smoothing processing to improve a color reproduction characteristic and an image free from a deteriorated gradation characteristic can be printed. Specifically, the smoothing processing improves the color reproduction characteristic. This smoothing processing may cause a color originally not having the lightness equal to or lower than blacking lightness to be converted to a color having lightness equal to or lower than the blacking lightness. To solve this, such a color is subjected to a gradation adjustment processing to convert the color to the color having the lightness higher than blacking lightness. A gamut mapping does not map such a color on a black point, thus preventing such a color from being broken by the blacking.