An image processing apparatus comprising: target temperature acquisition means for acquiring a target temperature; measuring means configured to obtain patch colorimetric values by measuring target patches of a plurality of colors formed on a medium using toners at a temperature other than the target temperature, and to obtain colorimetric values by measuring the medium under a light source which includes an ultraviolet range, estimation means for estimating target patch colorimetric values of said target patches of the plurality of colors formed on the medium using the toners for the target temperature, and image correction means for correcting image data of an image to be formed by color conversion of said image data based on the target patch colorimetric values estimated by said estimation means, wherein said estimation means includes: media-dependent variation correction means for correcting, based on said target temperature, said temperature other than the target temperature, and predetermined temperature-colorimetric characteristics of the medium which are based on said colorimetric values obtained by measuring the medium under the light source which includes the ultraviolet range, said patch colorimetric values obtained by said measuring means at the temperature other than the target temperature; and toner-dependent variation correction means for correcting, based on said target temperature, said temperature other than the target temperature, and predetermined temperature-colorimetric characteristics of the toners obtained by measuring reference patches of a plurality of colors using the toners under a light source which does not include any ultraviolet range, the patch colorimetric values corrected by said media-dependent variation correction means to obtain the estimated target patch colorimetric values. target temperature acquisition means for acquiring a target temperature; measuring means configured to obtain patch colorimetric values by measuring target patches of a plurality of colors formed on a medium using toners at a temperature other than the target temperature, and to obtain colorimetric values by measuring the medium under a light source which includes an ultraviolet range, estimation means for estimating target patch colorimetric values of said target patches of the plurality of colors formed on the medium using the toners for the target temperature, and image correction means for correcting image data of an image to be formed by color conversion of said image data based on the target patch colorimetric values estimated by said estimation means, wherein said estimation means includes: media-dependent variation correction means for correcting, based on said target temperature, said temperature other than the target temperature, and predetermined temperature-colorimetric characteristics of the medium which are based on said colorimetric values obtained by measuring the medium under the light source which includes the ultraviolet range, said patch colorimetric values obtained by said measuring means at the temperature other than the target temperature; and toner-dependent variation correction means for correcting, based on said target temperature, said temperature other than the target temperature, and predetermined temperature-colorimetric characteristics of the toners obtained by measuring reference patches of a plurality of colors using the toners under a light source which does not include any ultraviolet range, the patch colorimetric values corrected by said media-dependent variation correction means to obtain the estimated target patch colorimetric values. media-dependent variation correction means for correcting, based on said target temperature, said temperature other than the target temperature, and predetermined temperature-colorimetric characteristics of the medium which are based on said colorimetric values obtained by measuring the medium under the light source which includes the ultraviolet range, said patch colorimetric values obtained by said measuring means at the temperature other than the target temperature; and toner-dependent variation correction means for correcting, based on said target temperature, said temperature other than the target temperature, and predetermined temperature-colorimetric characteristics of the toners obtained by measuring reference patches of a plurality of colors using the toners under a light source which does not include any ultraviolet range, the patch colorimetric values corrected by said media-dependent variation correction means to obtain the estimated target patch colorimetric values.