Image forming apparatus

An image forming apparatus, comprising:

• an image carrier;
• a density sensor configured to detect a density measurement value of a toner pattern on the image carrier and a density measurement value of a surface of the image carrier;
• and
• a density correction unit configured to (a) perform a measurement process that measures a rotation period of the image carrier, and (b) determine a density measurement value of a surface of the image carrier at a forming position of the toner pattern on the basis of the rotation period, determine a density of the toner pattern on the basis of the density measurement value of the toner pattern and the determined density measurement value of the surface of the image carrier, and perform correction of a density characteristic on the basis of the determined density of the toner pattern;
• wherein in the measurement process, the density correction unit (a1) obtains density measurement values of a surface in a measurement section of the image carrier at a first round, (a2) calculates as section background data at the first round respective differences between the density measurement values at the first round and an average value of the density measurement values at the first round, (a3) obtains density measurement values of a surface at least in the measurement section of the image carrier at a second round, (a4) calculates as section background data at the second round respective differences between the density measurement values at the second round and an average value of the density measurement values at the second round in a specific section of which a length is identical to a length of the measurement section, and (a5) determines the rotation period on the basis of a correlation between the section background data at the first round and the section background data at the second round;
• and the measurement section is a part in a circulating direction of the image carrier.