8 March 1999 Real-time active range finder using light intensity modulation
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Abstract
We propose a new real-time active range finder system, which operates at a video frame rate. Our system consist of a laser line pattern marker, a rotating mirror, a camera with an optical narrow bandpass filter, and a pipe-lined image signal processor. The vertical laser line pattern is horizontally scanned by the video-synchronized rotating mirror. The pattern is modulated with alternating a monotone decreasing intensity function and a monotone increasing function. The bandpass filter selectively transmits the laser light to decrease the disturbance of background light. Depth images are obtained using the intensity ratio of successive video field images, the coordinates of each pixel, and the baseline length. The intensity ratio specifies a line pattern in a plane. Meanwhile, the coordinates of each pixel specify a line that goes through the pixel position on the CCD and the center of the lens. Depth is calculated as an intersection point on the specified plane and line. The image signal processor can perform the above calculation using LUTs within a video frame. In this paper, we evaluate the measurable range, precision, and color properties of our system. Experimental results show that a two meters measurable range is obtained wit a 50 mW laser power, the standard deviations of the depth images with 5 by 5 median filtering are about 1 percent of the measured depth, and the object color has little effect on the measured depth except when the reflectance of the object is very small.
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Takeo Azuma, Kenya Uomori, Atsushi Morimura, "Real-time active range finder using light intensity modulation", Proc. SPIE 3640, Three-Dimensional Image Capture and Applications II, (8 March 1999); doi: 10.1117/12.341067; https://doi.org/10.1117/12.341067
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