Abstract: An image forming apparatus includes a conveyor to convey a recording medium; an image forming device including a recording head to form a test pattern including a first mark and a pair of second marks; an imaging device; and a processor. The processor includes a pattern forming unit to cause the image forming device to form one of the first and second marks and form the other after the conveyor conveys the recording medium by a predetermined conveyance amount, a position detector to detect positions of the first and second marks in the captured image, a ratio calculator to calculate a ratio between a distance between the second marks and deviation of the first mark in the captured image, and a distance calculator to calculate an actual distance of the deviation based on a theoretical distance between the second marks and the ratio.

Abstract: An imaging device includes an imaging unit to obtain a captured image of a test pattern and a reference mark to locate the test pattern and at least one processor. The test pattern includes a pair of first marks and a second mark. The processor includes a position detector configured to detect the reference mark in the captured image and locate the pair of first marks and the second mark in the captured image, and a ratio calculator configured to calculate one of a first ratio between a distance between the pair of first marks in the captured image and a deviation of the second mark in the captured image, and a second ratio between the distance between the pair of first marks in the captured image and a distance from one of the pair of first marks to the second mark in the captured image.