1. An image processing apparatus comprising: a patch forming unit that forms a plurality of mixed-color patches by superposing single color patches of a plurality of colors with different gradation ratios according to gradation values; a color measuring unit that performs color measurement of the mixed-color patches; an estimating unit that estimates color values of single colors present in the mixed-color patches based on color measurement values obtained by performing color measurement; and a correction table setting unit that sets a correction table in order to correct the estimated color values of the single colors to target color values.