US Patent 7641310 Image processing apparatus, printing apparatus and image processing method

Lattice point data of each lattice point on W-C line in a color separation table reproducing primary color C is determined so that C ink monotonically increases from W point to C point. Also, particular color G for toning is used to monotonically increase from the halfway of W point to C point and lattice point data is determined so that the basic color C ink and the particular color G ink are mixed at C point. In a case where the reflection characteristics is made such that the basic color C ink thus produces the coloring closer to a blue color, the particular color G ink having high chroma and many portions overlapped in the zone of the C ink and the green color is used at a high density portion of the device primary color C. This realizes control of the hue shift and the high chroma both.