Image forming apparatus and density unevenness detection method

摘要

A plurality of test patches each including a dark and light image which has density unevenness of a predetermined period in which the plurality of test patches are differentiated in phase difference relative to a phase of density unevenness induced by rotational unevenness occurring at a predetermined period in the motor for driving a photosensitive drum is formed. Then, density information of the plurality of test patches with is detected by a density sensor 41, and the phase of the density unevenness is obtained based on detection results (density information) of the plurality of test patches as well as based on a phase difference corresponding to a test patch whose density unevenness is a predetermined value in amplitude.