1. A method for deriving spectral sensitivity characteristics of a color image input device, comprising: a step of setting a constraint that tristimulus values of metamer data perceived to be the same in color by observation in a color matching evaluation experiment are made equal, to said metamer data; a step of obtaining a third objective function by assigning weights to a first objective function including a standard color matching function and to a second objective function in a uniform color space and by binding these two objective functions together; a step of obtaining, by using the method of Lagrange multipliers, a correcting color matching function used for correction to make said third objective function minimum under said constraint; a step of obtaining an amended color matching function to be amended based on a sum of said obtained correcting color matching function and said standard color matching function; and a step of obtaining spectral sensitivity characteristics amended by using said amended color matching function.