Patches to be measured are formed (S110), density of each formed patch is measured (S120), and density of patches that are not formed is estimated from the measured density values using correspondence data representing correlation between density measurements of patches of a specific tone and density measurements of patches of tones other than the specific tone (S130). Density values for all tones are then calculated from the acquired density data by interpolation (S140) to produce correction data (calibration data) (S150). Thus estimating the density of unformed patches enables reducing a number of patches to be formed, and therefore reduces time required to form and measure the patches.