1. A method of calculating a color conversion matrix for allowing color data in a first color space regarding a plurality of color patch data to correspond to color data in a second color space, comprising the steps of: forming a pseudo inverse matrix of a matrix constructed by the color data in said first color space when the number of said color patch data does not coincide with the total number of components of said color conversion matrix; and calculating said color conversion matrix by using said pseudo inverse matrix and a matrix constructed by the color data in said second color space.