Patent ID: 8310734

Claim:
An image forming apparatus comprising: a forming unit configured to form a mark on a carrier and including a plurality of forming units, each forming unit configured to form respective marks in respective colors different from each other; a light emitting unit configured to emit light toward a surface of the carrier; a light receiving unit configured to receive reflected light from the surface of the carrier and from the mark and to output a light reception signal corresponding to an amount of the received reflected light; a processor; and memory storing computer readable instructions that, when executed, cause the image forming apparatus to: detect a position of the mark on the carrier based on a signal wave included in the light reception signal; modify the detected position of the mark by a modification amount corresponding to a difference in a waveform of the signal wave corresponding to the mark so as to reduce an error between the detected position and an actual position; recognize which mark the signal wave included in the light reception signal corresponds to based on information on a process of forming the marks by the forming unit; and determine the difference in the waveform of the signal wave based on the color, shape, and size of the mark corresponding to the signal wave.