An image processing apparatus comprising: measurement means for reading a patch image for a calibration, the patch image being plural patches that have been printed at different densities on a recorded medium of an unidentified type by a printing apparatus using colorants included therein, and measuring the densities of the patch image by using a light source having a peak at one wavelength and light receiving means for receiving reflection light generated when the recorded medium is irradiated by the light source, the light source and light receiving means being comprised in the measurement means; reception means for receiving spectral reflection factor information for each of said colorants measured by reading the patch image for the calibration printed on the recorded medium by the printing apparatus or on a recorded medium of a same type by another printing apparatus, by using a measurement device capable of emitting white light and measuring a spectral reflection factor at every one of predetermined wavelengths; processing means for performing a calibration for a printing using the recorded medium of the unidentified type by the printing apparatus on the basis of the densities measured by the measurement means, a correction value for the recorded medium of the unidentified type, and predetermined reference density values, so that the densities measured are corrected to have the reference density values; and correction means for performing, as part of the calibration, a calculation to acquire the correction value for the recorded medium of the unidentified type, on the basis of actual measurement information indicating a light reception characteristic of the measurement means which is based on an emission spectroscopy characteristic of the light source and a light reception sensitivity characteristic of the light receiving means, predetermined reference information indicating a reference light reception characteristic, and the spectral reflection factor information received by the reception means, in a manner that the light reception characteristic of the measurement means becomes equal to the reference light reception characteristic. measurement means for reading a patch image for a calibration, the patch image being plural patches that have been printed at different densities on a recorded medium of an unidentified type by a printing apparatus using colorants included therein, and measuring the densities of the patch image by using a light source having a peak at one wavelength and light receiving means for receiving reflection light generated when the recorded medium is irradiated by the light source, the light source and light receiving means being comprised in the measurement means; reception means for receiving spectral reflection factor information for each of said colorants measured by reading the patch image for the calibration printed on the recorded medium by the printing apparatus or on a recorded medium of a same type by another printing apparatus, by using a measurement device capable of emitting white light and measuring a spectral reflection factor at every one of predetermined wavelengths; processing means for performing a calibration for a printing using the recorded medium of the unidentified type by the printing apparatus on the basis of the densities measured by the measurement means, a correction value for the recorded medium of the unidentified type, and predetermined reference density values, so that the densities measured are corrected to have the reference density values; and correction means for performing, as part of the calibration, a calculation to acquire the correction value for the recorded medium of the unidentified type, on the basis of actual measurement information indicating a light reception characteristic of the measurement means which is based on an emission spectroscopy characteristic of the light source and a light reception sensitivity characteristic of the light receiving means, predetermined reference information indicating a reference light reception characteristic, and the spectral reflection factor information received by the reception means, in a manner that the light reception characteristic of the measurement means becomes equal to the reference light reception characteristic.