| 摘要 |
PROBLEM TO BE SOLVED: To output an evaluation chart whereby a phase shift in a horizontal scanning direction among a plurality of light beams in an imaging region can be detected with a high sensitivity simply. SOLUTION: There are provided a first pattern in which a dot string by the next beam is arranged while shifted in the horizontal scanning direction with respect to a dot string by a predetermined beam formed in the horizontal scanning direction, and a second pattern in which a dot string by the next beam is arranged while shifted in a direction opposite to the shift direction of the first pattern in the horizontal scanning direction with respect to a dot string formed by a predetermined beam in the horizontal scanning direction. The evaluation chart is outputted having a first pattern group in which the first pattern is repeated by a period of an integral multiple of the number of the light beams in a vertical scanning direction and is also repeated at constant intervals in the horizontal scanning direction, and a second pattern group in which the second pattern is repeated by the period of the integral multiple of the number of the light beams in the vertical scanning direction and is also repeated at constant intervals in the horizontal scanning direction.
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