1. An image processing apparatus comprising: a first pattern generation unit configured to cause an image forming section to generate a plurality of image patterns that are obtained by correcting predetermined image data using each of a plurality of correction parameters, wherein the plurality of correction parameters have periodicity unique to the image forming section and are mutually different in phase; a first selection unit configured to select one phase corresponding to a test pattern from the plurality of image patterns generated by the first pattern generation unit; a second pattern generation unit configured to cause the image forming section to generate a plurality of image patterns that are obtained by correcting predetermined image data using each of a plurality of correction parameters, wherein the plurality of correction parameters have the phase selected by the first selection unit and are mutually different in amplitude; a second selection unit configured to select one amplitude corresponding to a test pattern from the plurality of image patterns generated by the second pattern generation unit; and an image correction unit configured to correct an image based on a phase selected by the first selection unit and an amplitude selected by the second selection unit.