"Absolute three-dimensional shape measurement using coded fringe patterns without phase unwrapping or projector calibration," Opt. Express, (2014)

[65] W. Lohry*, V. Chen*, and S.  Zhang,  "Absolute three-dimensional shape measurement using coded fringe patterns without phase unwrapping or projector calibration," Opt. Express 22(2), 1287-1301, 2014; doi:10.1364/OE.22.001287

Abstract

This paper presents a novel stereo-phase-based absolute three-dimensional (3D) shape measurement that requires neither phase unwrapping nor projector calibration. This proposed method can be divided into two steps: (1) obtain a coarse disparity map from the quality map; and (2) refine the disparity map using wrapped phase. Fringe patterns are modified to encode the quality map for efficient and accurate stereo matching. Experiments demonstrated that the proposed method could achieve high-quality 3D measurement even with extremely low-quality fringe patterns.
 

"Structured light system calibration method with optimal fringe angle," Appl. Opt., (2014)

B. Li* and S. Zhang, "Structured light system calibration method with optimal fringe angle," Appl. Opt., 53(13), 7942-7950, 2014 (Cover feature); doi: 10.1364/AO.53.007942

Abstract

For structured light system calibration, one popular approach is to treat the projector as an inverse camera. This is usually performed by projecting horizontal and vertical sequences of patterns to establish one-to-one mapping between camera points and projector points. However, for a well-designed system, either horizontal or vertical fringe images are not sensitive to depth variation and thus yield inaccurate mapping. As a result, the calibration accuracy is jeopardized if a conventional calibration method is used. To address this limitation, this paper proposes a novel calibration method based on optimal fringe angle determination. Experiments demonstrate that our calibration approach can increase the measurement accuracy up to 38% compared to the conventional calibration method with a calibration volume of 300
H mm × 250
W mm × 500
D mm. 

"High-Speed 3-D Optical Metrology and Applications," Opt. Eng., (2014)

S. Zhang, R. Liang, and L. Yang, "High-speed 3D optical metrology and applications," Opt. Eng. 53(11), 112201, 2014 (Special Section Guest Editorial); doi:10.1117/1.OE.53.11.112201

"High-speed absolute three-dimensional shape measurement using three binary dithered patterns," Opt. Express, (2014)

[69]  W. Lohry* and S. Zhang, "High-speed absolute three-dimensional shape measurement using three binary dithered patterns," Opt. Express 22(22), 26752-26762, 2014 (Cover feature) (Image of the week of Nov. 22, 2014, OSA Optics InfoBase); doi: 10.1364/OE.22.026752

Abstract

This paper describes a method to reconstruct high-speed absolute three-dimensional (3D) geometry using only three encoded 1-bit binary dithered patterns. Because of the use of 1-bit binary patterns, high-speed 3D shape measurement could also be achieved. By matching the right camera image pixel to the left camera pixel in the object space rather than image space, robust correspondence can be established. Experiments demonstrate the robustness of the proposed algorithm and the potential to achieve high-speed 3D shape measurements.

"High-speed absolute three-dimensional shape measurement using three binary dithered patterns," Opt. Express, (2014)

[69]  W. Lohry* and S. Zhang, "High-speed absolute three-dimensional shape measurement using three binary dithered patterns," Opt. Express 22(22), 26752-26762, 2014 (Cover feature) (Image of the week of Nov. 22, 2014, OSA Optics InfoBase); doi: 10.1364/OE.22.026752

Abstract

This paper describes a method to reconstruct high-speed absolute three-dimensional (3D) geometry using only three encoded 1-bit binary dithered patterns. Because of the use of 1-bit binary patterns, high-speed 3D shape measurement could also be achieved. By matching the right camera image pixel to the left camera pixel in the object space rather than image space, robust correspondence can be established. Experiments demonstrate the robustness of the proposed algorithm and the potential to achieve high-speed 3D shape measurements.

"Superfast 3D optical sensing using fiber interference", SPIE Newsroom, 2014

B. Li*, S. Zhang and P. Ou, "Superfast 3D optical sensing using fiber interference," SPIE Newsroom, doi: 10.1117/2.1201408.005584, 2014 (invited)

Incorporating a lithium niobate electro-optic phase modulator into an interferometric fringe projection system could permit imaging at rates of megahertz or even gigahertz.

 

"Virtual tool mark generation for efficient striation analysis," J. Forensic Sci., (2014)

[62] L. Ekstrand*, S. Zhang, T. Grieve, L. S. Chumbley, and J. Kreiser, "Virtual tool mark generation for efficient striation analysis," J. Forensic Sci., 59(4), 950-959, 2014; doi:10.1111/1556-4029.12435

"Novel calibration method for structured light system with an out-of-focus projector," Appl. Opt. 2014

B. Li*, N. Karpinsky*, and S. Zhang, "Novel calibration method for structured light system with an out-of-focus projector,"Appl. Opt. 53(13), 3415-3426, 2014; doi: 10.1364/AO.53.003415

A structured-light system with a binary defocusing technique has the potential to have more extensive application due to its high speeds, gamma-calibration-free nature, and lack of rigid synchronization requirements between the camera and projector. However, the existing calibration methods fail to achieve high accuracy for a structured-light system with an out-of-focus projector. This paper proposes a method that can accurately calibrate a structured-light system even when the projector is not in focus, making it possible for high-accuracy and high-speed measurement with the binary defocusing method. Experiments demonstrate that our calibration approach performs consistently under different defocusing degrees, and a root-mean-square error of about 73 μm can be achieved with a calibration volume of 150
H mm × 250
W mm × 200
D mm. 

"Towards superfast three-dimensional optical metrology with digital micromirror device (DMD) platforms," Opt. Eng., (2015)

[67] T. Bell* and S. Zhang, "Towards superfast three-dimensional optical metrology with digital micromirror device (DMD) platforms," Opt. Eng., 53(11), 112206, 2014; doi: 10.1117/1.OE.53.11.112206

Decade-long research efforts toward superfast three-dimensional (3-D) shape measurement leveraging the digital micromirror device (DMD) platforms are summarized. Specifically, we will present the following technologies: (1) high-resolution real-time 3-D shape measurement technology that achieves 30 Hz simultaneous 3-D shape acquisition, reconstruction, and display with more than 300,000 points per frame; (2) superfast 3-D optical metrology technology that achieves 3-D measurement at a rate of tens of kilohertz utilizing the binary defocusing method we invented; and (3) the improvement of the binary defocusing technology for superfast and high-accuracy 3-D optical metrology using the DMD platforms. Both principles and experimental results are presented.

"High-resolution, real-time three-dimensional shape measurement on graphics processing unit," Opt. Eng., (2014)

[64] N. Karpinsky*, M. Hoke*, V. Chen*, and S.  Zhang, "High-resolution, real-time three-dimensional shape measurement on graphics processing unit," Opt. Eng. 53(2), 024105, 2014;  doi: 10.1117/1.OE.53.2.024105

Abstract

A three-dimensional (3-D) shape measurement system that can simultaneously achieve 3-D shape acquisition, reconstruction, and display at 30 frames per second (fps) with 480,000 measurement points per frame is presented. The entire processing pipeline was realized on a graphics processing unit (GPU) without the need of substantial central processing unit (CPU) power, making it achievable on a portable device, namely a laptop computer. Furthermore, the system is extremely inexpensive compared with similar state-of-art systems, making it possible to be accessed by the general public. Specifically, advanced GPU techniques such as multipass rendering and offscreen rendering were used in conjunction with direct memory access to achieve the aforementioned performance. The developed system, implementation details, and experimental results to verify the performance of the proposed technique are presented.

"Digital micromirror transient response influence on superfast 3D shape measurement," Opt. Laser Eng., (2014)

[63] Y. Wang*, B.  Bhattacharya, E. H. Winer, P. Kosmicki, W. H. El-Ratal, and S. Zhang, "Digital micromirror transient response influence on superfast 3D shape measurement," Opt. Laser Eng. 58, 19-26, 2014; doi: 10.1016/j.optlaseng.2014.01.015

Abstract

Nowadays, the high speed (e.g., kilo-Hertz) refreshing rate of the digital micro-mirror device (DMD) has enabled superfast 3D shape measurement using the binary defocusing technique. This research finds that when the system reaches its extreme binary pattern refreshing rate, the transient response of the DMD induces a coupling effect (i.e., two neighboring patterns blend together) that may cause substantial measurement error. Since this transient response repeats itself, this systematic measurement error is substantially reduced to a negligible level when the timing between the projector and the camera is properly adjusted. Experimental results are presented to demonstrate the observed phenomena, and the success of utilizing the proposed method to overcome the problems associated with the transient response of the DMD.

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

[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.

"Objective comparison toolmarks from the cutting surfaces of slip-joint pliers," AFTE Journal, (2014)

[57] T. Grieve, L. S. Chumbley, J. Kreiser, M. Morris,  L. Ekstrand*, and S. Zhang, "Objective comparison toolmarks from the cutting surfaces of slip-joint pliers," AFTE Journal  46(2), 176-185, 2014

Abstract

Experimental results from a statistical analysis algorithm for objectively comparing toolmarks via data files obtained using optical profilometry data are described. The algorithm employed has successfully been used to compare striated marks produced by screwdrivers. In this study, quasi-striated marks produced by the cutting surfaces of slip-joint pliers were examined. Marks were made by cutting both copper and lead wire. Data files were obtained using an optical profilometer that uses focus variation to determine surface roughness. Early efforts using the comparative algorithm yielded inconclusive results when the comparison parameters used were the same as those employed successfully for screw-driver marks. Further experiments showed that the algorithm could successfully be used to separate known matches from non-matches by changing the comparison parameters. Results are presented from the analysis of the copper wires.

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

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

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

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.