Image forming apparatus controlling timing of forming measurement image based on prior measurements and density of image to be formed

An image forming apparatus, comprising:

• an image forming unit configured to form an image on a sheet based on an image forming condition;
• a sensor configured to measure measurement images formed by the image forming unit;
• and
• a controller configured to:
• control the image forming condition based on a measurement result of measuring a first measurement image by the sensor;
• acquire information having a correlation to density variation of images to be formed by the image forming unit;
• control the image forming condition based on the information;
• determine a first value regarding a density of an image to be formed by the image forming unit, based on a measurement result of measuring a second measurement image by the sensor;
• determine a second value regarding a density of the image to be formed by the image forming unit, based on the information;
• and
• control a timing at which the image forming unit next forms the first measurement image, based on the first value and the second value.