Image-forming apparatus that acquires passage times of color developers

A non-transitory storage medium storing a computer program for causing a computer in an image-forming apparatus to execute an acquisition process, the image-forming apparatus including multiple developing units configured to form images using multiple color developers whose colors are mutually different, an image carrier configured to, in color displacement detection, carry the multiple color developers transferred thereon from the multiple developing units at mutually different image-carrying positions, and an optical sensor configured to project a light to the image carrier and receive a reflected light from the image carrier, the acquisition process acquiring, in response to output from the optical sensor, passage times at which the multiple color developers carried by the image carrier respectively pass a detection position, the acquisition process comprising:

• a process to acquire output from the optical sensor that receives a diffusively reflected light from a non-transferred area of the image carrier on which the developers are not transferred;
• and
• a process to acquire the passage times of all the multiple color developers, in response to changes in the output from the optical sensor at an output level higher than that corresponding to a diffusively reflected light from the developers on the image carrier,
• wherein the received diffusively reflected light amount from the nontransferred area of the image carrier is larger than that from the developers on the image carrier due to a position of a light-receiving portion of the optical sensor.