"Absolute three-dimensional shape measurement with a known object," Optics Express (2017)

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J. Dai and S. Zhang, "Absolute three-dimensional shape measurement with a known object," Opt. Express25(9), 10384-10396 (2017); doi: 10.1364/OE.25.010384

Abstract

This paper presents a novel method for absolute three-dimensional (3D) shape measurement that does not require conventional temporal phase unwrapping. Our proposed method uses a known object (i.e., a ping-pong ball) to provide cues for absolute phase unwrapping. During the measurement, the ping-pong ball is positioned to be close to the nearest point from the scene to the camera. We first segment ping-pong ball and spatially unwrap its phase, and then determine the integer multiple of $2\pi$ to be added such that the recovered shape matches its actual geometry. The nearest point of the ball provides $z_{min}$ to generate the minimum phase $\Phi_{min}$ that is then used to unwrap phase of the entire scene pixel by pixel. Experiments demonstrated that only three phase-shifted fringe patterns are required to measure absolute shapes of objects moving along depth $z$ direction.

"Three-dimensional shape measurement with dual reference phase maps, " Opt. Eng. ,(2014)

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[58] J. Dai, C. Gong*, and S. Zhang, "Three-dimensional shape measurement with dual reference phase maps, " Opt. Eng. 53(1), 014102, 2014; doi: 10.1117/1.OE.53.1.014102

Abstract

Single reference-phase-based methods have been extensively utilized in digital fringe projection systems, yet they might not provide the maximum sensitivity given a hardware system configuration. This paper presents an innovative method to improve the measurement quality by utilizing two orthogonal phase maps. Specifically, two reference phase maps generated from horizontal and vertical (i.e., orthogonal) fringe patterns projected are combined into a vector reference phase map through a linear combination for depth extraction. The experiments have been conducted to verify the superiority of the proposed method over a conventional single reference-phase-based approach.

"Intensity-optimized dithering technique for high-quality 3d shape measurement," Opt. Laser Eng., 2014

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J. Dai, B. Li*, and S. Zhang, "Intensity-optimized dithering technique for high-quality 3d shape measurement," Opt. Laser Eng. 53, 79-85, 2014; doi: 10.1016/j.optlaseng.2013.08.015

Our previously proposed phase-based optimization method [1] has proven successful in improving the measurement quality when a dithering technique is used. This paper presents an intensity-based optimization method for 3D shape measurement with binary dithering techniques. Both simulations and experiments find that the phase-based optimization method can generate high-quality phase under a given condition, but it is sensitive to the amount of defocusing. In contrast, the proposed intensity-based optimization method can consistently generate high-quality phase with various amounts of defocusing.

"Some recent advances on superfast 3D shape measurement with digital binary defocusing techniques," Opt. Laser Eng. 2014

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B. Li*, Y. Wang*, J. Dai, and W. Lohry*, and S. Zhang, "Some recent advances on superfast 3D shape measurement with digital binary defocusing techniques," Opt. Laser Eng. 54, 236-246, 2014 (invited); doi:10.1016/j.optlaseng.2013.07.010

The digital binary phase-shifting technique has been demonstrated for its merits over the conventional sinusoidal phase-shifting method in terms of measurement speed and simplicity. Yet, the measurement depth range is small when a squared binary method is used. Our recent research focuses on improving its measurement accuracy without sacrificing measurement speed, and increasing its depth range without losing measurement quality. This paper will summarize our recent work on the following three major areas: (a) realization of kHz 3D shape measurement with binary phase-shifting methods; (b) binary pattern improvement with pulse width modulation and binary dithering/halftoning techniques; and (c) applications of superfast 3D shape measurement techniques. Principle of each technique will be presented, and experimental results will be shown to verify its performance.

"High-quality fringe pattern generation using binary pattern optimization through symmetry and periodicity," Opt. Laser Eng., 2014

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J. Dai, B. Li*, and S. Zhang, "High-quality fringe pattern generation using binary pattern optimization through symmetry and periodicity," Opt. Laser Eng., 52, 195-200, 2014; doi: 10.1016/j.optlaseng.2013.06.010

This paper presents a novel method to construct binary patterns for high-quality 3D shape measurement. The algorithm generates small patches using symmetry and periodicity, randomly initializes each pixels, optimizes the small patches through mutations, and finally tiles the optimized patches into full size patterns using again symmetry and periodicity. We will demonstrate that the proposed method can achieve substantial phase quality improvements over the dithering techniques for different amounts of defocusing.

"Phase-optimized dithering technique for high-quality 3D shape measurement," Opt. Laser Eng., (2013)

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[51] J. Dai and S. Zhang, "Phase-optimized dithering technique for high-quality 3D shape measurement," Opt. Laser Eng. 51(6), 790-795, 2013; doi: 10.1016/j.optlaseng.2013.02.003

Abstract

Our recent study showed that the Bayer-dithering technique could substantially improve 3D measurement quality for the binary defocusing method. Yet, the dithering technique was developed to optimize the appearance or intensity representation, rather than the phase, of an image. This paper presents a framework to optimize the Bayer-dithering technique in phase domain by iteratively mutating the status (0 or 1) of a binary pixel. We will demonstrate that the proposed optimization technique can drastically reduce the phase error when the projector is nearly focused.