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10 September 2009 Combined stereovision and phase shifting method: use of a color-coded visibility-modulated fringe pattern
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The use of a color visibility-modulated fringe pattern is proposed to further accelerate image acquisition in the newly proposed combined stereovision and phase shifting method for 3-D shape measurement. The method uses two cameras and one projector and can eliminate errors caused by inaccurate phase measurement. In order to eliminate the need for pattern switching and thus make real-time image acquisition possible, the use of a visibility-modulated fringe pattern was previously proposed. This modified pattern is sinusoidal in one direction as in a conventional fringe pattern, but is visibility-modulated in the other direction. Using this modified pattern we can achieve pixel-level phase matching in both directions without changing the fringe pattern. In this paper, a color visibility-modulated fringe pattern is introduced to further accelerate image acquisition. To obtain the three fringe images simultaneously, we encode the three phase-shifted fringe patterns into the R, G, and B channels of a color pattern and project it onto the object via a color projector. The color fringe image is then taken by two single-CCD color cameras simultaneously and each decoded into three fringe images. The problems specifically associated with color systems, such as color coupling and color imbalance, will be shown to have much less effect on the measured results. With this technique, the acquisition speed is limited only by the frame rate of the camera, which significantly reduces the errors caused by object motions. Experimental results are presented to support claims of the proposed method.
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Xu Han, Peisen Huang, Zhicheng Deng, and Leon Xu "Combined stereovision and phase shifting method: use of a color-coded visibility-modulated fringe pattern", Proc. SPIE 7432, Optical Inspection and Metrology for Non-Optics Industries, 74320X (10 September 2009);


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