US Patent 7417651 Image forming apparatus

A registration mark is a toner image which has a first linear pattern and a second linear pattern, which extend along a main scanning direction, and a two-dimensional pattern. The first linear pattern, the two-dimensional pattern and the second linear pattern are arranged apart from each other in this order along a transporting direction. In short, the linear patterns and extending along the main scanning direction are formed spaced apart from the two-dimensional pattern, one toward the upstream side and the other toward the downstream side, along the transporting direction. This suppresses the edge effect along the transporting direction and realizes accurate detection of the position of each registration mark by a test pattern sensor.