| 摘要 |
A photoelectric sensor includes a light-emitting element and a light-receiving element and detects a mark on an object. Prior to the detection of the mark, a reference received light quantity level is sampled for the surface of an object not including the mark, for every color of light. A mark received light quantity level is then sampled for every color of light. The difference is obtained between the reference received light quantity level and the corresponding mark received light quantity level for each color of light. A ratio of the obtained difference to the reference received light quantity level is obtained. For the colors of light where the difference equals or exceeds a predetermined value, the color of light having the largest ratio is selected for emission from the light-emitting element in the detection of the mark.
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