Image Forming Apparatus

An image forming apparatus, comprising:

• an image forming unit which includes a container unit for containing a developing agent and an agitation unit for agitating the developing agent contained in the container unit, the image forming unit performing image formation using the developing agent;
• a sensor which includes a light emitting unit configured to emit light toward the container unit and a light receiving unit configured to receive the light emitted from the light emitting unit and passing through the container unit, the sensor generating an output in accordance with an amount of light received by the light receiving unit while the agitation unit agitates the developing agent;
• a storage unit;
• a processing unit;
• memory having machine readable instructions stored thereon that, when executed by the processing unit, perform the steps of:
• calculating a measurement result based on the output generated by the sensor;
• determining, after the agitation is started, whether a current period is an unstable period in which the measurement result is unstable or a stable period in which the measurement result is stable;
• and
• storing the measurement result in the storage unit during the stable period;
• during the stable period, detecting an amount of remaining developing agent in accordance with the latest measurement result based on the latest output generated by the sensor;
• and
• during the unstable period, detecting the amount of remaining developing agent in accordance with a previous measurement result stored in the storage unit.