1. An image processing method of processing an image data being presented in a color space that is defined with color components of three colors, the method comprising: mapping a first part and a second part of color signal to an achromatic axis defined on the basis of an arbitrary illuminant, wherein one color is saturated in the first part of the signal and two colors are saturated in the second part of the signal; and mapping a surround color signal surrounding the saturated color signal so as to preserve chroma gradations of the surround color signal, toward the achromatic axis.