Importance

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Abstract

An object whose position is to be measured is provided with a light-emitting element, the luminance of the light-emitting element is varied in two levels (lit/extinguished) with a prescribed period, images of four consecutive frames are successively acquired, one frame being an image picked up in a time of 1/4 of the period of this variation of luminance, of the four consecutive frames, a first difference image of the first frame and third frame and a second difference image of the second frame and fourth frame are acquired, and, of the first difference image and second difference image, the difference image of greatest lightness is selected. This selected difference image is always the difference image between the image during the lit period of the light-emitting element and the image during the extinguished period. Pixels whose lightness is greater than a prescribed threshold value in this selected difference image is detected as the position of the light-emitting element, and the position relative to the object is thereby calculated.

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First Claim