The present invention provides a mechanism that more appropriately evaluates an image defect caused by a specific process in an image forming apparatus. An image forming apparatus of this invention performs colorimetry of a patch image at a spatial resolution corresponding to the spatial frequency of color unevenness caused by a specific process included in an image forming process. A statistic value based on the n-th (n is an integer of 2 or more) order central moment of a specific color component of a colorimetric value obtained by performing colorimetry at the spatial resolution is compared with a reference value, thereby detecting that the color unevenness caused by the specific process has occurred in the patch image.