Color values of output colors reproduced based on output values corresponding to input values of grid points in an input color space, which are obtained by sampling a range of the output values, are estimated. Changes between a color value estimated in correspondence with an input value of a grid point of interest and color values estimated in correspondence with input values of adjacent grid points, changes between an output value of the interest point and output values of the adjacent points, and changes between a plurality of color values estimated in correspondence with input values to the interest point in association with different light sources are evaluated. When the input value of the interest point, whose a sum of evaluation values of these evaluations is less than a threshold, is obtained, an output value corresponding to that input value is set in the interest point.