Image forming apparatus using a plurality of toner patches during a non-printing period

An image forming apparatus comprising:

• an image carrier;
• a toner-image forming device configured to form a toner image on the image carrier;
• a controller configured to control the toner-image forming device to form a toner patch;
• a detector configured to detect the toner patch on the image carrier;
• and
• a developing unit including a developing roller, wherein
• during a non-printing period, the controller causes the toner-image forming device to form a plurality of toner patches, causes the detector to detect densities of the plurality of toner patches, and adjusts an image-forming condition of the toner-image forming device based on detected densities, and
• during a printing period, the controller causes the toner-image forming device to form an output image in an image area and form fewer toner patches in a non-image area, causes the detector to detect densities of the fewer toner patches, and adjusts the image-forming condition of the toner-image forming device based on detected densities, the fewer toner patches being selected from and fewer than the plurality of toner patches formed during the non-printing period.