1. A color space transformation matrix calculating method that calculates a color space transformation matrix which transforms colors in a first color space to colors in a second color space, the method comprising: optimizing a plurality of constant color-space transformation matrices, so that each of said constant color-space transformation matrices is adjusted to transform each standard color in said first color space to each goal color in said second color space, which correspond to each said standard color, wherein the optimizing includes: calculating displacement of each matrix element based on conditions for a merit function such that the merit function takes a minimum value, the merit function being defined in a uniform color space, and renewing each matrix element repeatedly until the merit function is determined to have a value below or equal to a predetermined threshold value; and calculating interpolation functions for each matrix element of a color-space transformation matrix applied for the entire range of colors of said first color space, based on said constant color-space transformation matrices, wherein the interpolation functions are functions including a coordinate of a predetermined coordinate system of said uniform color space, as an independent variable.