Image forming apparatus

An image forming apparatus, comprising:

• an image carrier configured to carry a toner pattern;
• a sensor that comprises a light emitter and a photodetector, the light emitter configured to output light with which the toner pattern or a surface material of the image carrier is irradiated, the photodetector configured to receive reflection light from the toner pattern or the surface material of the image carrier;
• a sensor light intensity control unit configured to provide a control voltage to the light emitter and thereby control light intensity of the light emitter;
• and
• a density determining unit configured to determine a toner density on the basis of output of the photodetector;
• wherein the density determining unit (a) determines as a correction parameter a first-order coefficient of a control voltage of the light emitter for an output voltage of the photodetector corresponding to reflection light from the surface material of the image carrier, (b) determines a correction amount corresponding to the correction parameter and the toner density, and (c) corrects the toner density on the basis of the correction amount.