"Pixel-by-pixel absolute three-dimensional shape measurement with modified Fourier transform profilometry" Appl. Opt., (2017)

[95] H. Yun, B. Li, and S. Zhang, "Pixel-by-pixel absolute three-dimensional shape measurement with modified Fourier transform profilometry", Appl. Opt., 56(5), 1472-1480, (2017); doi: 10.1364/AO.56.001472

Abstract

Single-pattern Fourier transform profilometry (FTP) method and double-pattern modified FTP method have great value on high-speed three-dimensional (3D) shape measurement, yet it is difficult to retrieve absolute phase pixel by pixel. This paper presents a method that can recover absolute phase pixel by pixel for the modified FTP method. The proposed method uses two images with different frequencies, and the recovered low frequency phase is used to temporally unwrap the high-frequency phase pixel by pixel. This paper also presents the computational framework to reduce noise impact for robust phase unwrapping. Experiments demonstrate the success of the proposed absolute phase recovery method using only two fringe patterns.

"Development of a mobile tool mark characterization/comparison system," J. Forensic Sci., (2017)

L. S. Chumbley,  M. Morris, R. Spotts, and C. Macziewski, "Development of a mobile tool mark characterization/comparison system," J. Forensic Sci., 62(1), 83-91 (2017), doi: 10.1111/1556-4029.13233

Since the development of the striagraph, various attempts have been made to enhance forensic investigation through the use of measuring and imaging equipment. This study describes the development of a prototype system employing an easy-to-use software interface designed to provide forensic examiners with the ability to measure topography of a toolmarked surface and then conduct various comparisons using a statistical algorithm. Acquisition of the data is carried out using a portable 3D optical profilometer, and comparison of the resulting data files is made using software named “MANTIS” (Mark and Tool Inspection Suite). The system has been tested on laboratory-produced markings that include fully striated marks (e.g., screwdriver markings), quasistriated markings produced by shear-cut pliers, impression marks left by chisels, rifling marks on bullets, and cut marks produced by knives. Using the system, an examiner has the potential to (i) visually compare two toolmarked surfaces in a manner similar to a comparison microscope and (ii) use the quantitative information embedded within the acquired data to obtain an objective statistical comparison of the data files. This study shows that, based on the results from laboratory samples, the system has great potential for aiding examiners in conducting comparisons of toolmarks.

"Evaluation of pixel-wise geometric constraints based phase unwrapping method for low signal-to-noise-ratio (SNR) phase," Advanced Optical Technologies, (2016)

[91] Y. An, Z. Liu and S. Zhang, "Evaluation of pixel-wise geometric constraints based phase unwrapping method for low signal-to-noise-ratio (SNR) phase," Advanced Optical Technologies, 5(5-6), 423–432, (2016); doi: 10.1515/aot-2016-0048

This paper evaluates the robustness of our recently proposed geometric constraints based phase unwrapping method to unwrap low signal-to-noise ratio (SNR) phase.  Instead of capturing additional images for absolute phase unwrapping, the new phase unwrapping algorithm uses geometric constraints of the digital fringe projection (DFP) system to create a virtual reference phase map to unwrap the phase pixel by pixel. Both simulation and experimental results demonstrate that this new phase unwrapping method can even successfully unwrap low SNR phase maps that brings difficulties for conventional multi-frequency phase unwrapping methods.

"A self-recalibration method based on scale-invariant registration for structured light measurement systems," Opt. Laser Eng., (2017)

[92] R. Chen, J. Xu, S. Zhang, H. Chen, Y. Guan, and K. Chen, "A self-recalibration method based on scale-invariaant registration for structured light measurement systems," Opt. Laser Eng., 88, 75-81 (2017); doi:10.1016/j.optlaseng.2016.07.003

Abstract

The measurement accuracy of structured light measurement depends on delicate offline calibration. However, in some practical applications, the system is supposed to be reconfigured so frequently to track the target that an online calibration is required. To this end, this paper proposes a rapid and autonomous self-recalibration method. For the proposed method, first, the rotation matrix and normalized translation vector are attained from the fundamental matrix; second, the scale factor is acquired based on scale-invariant registration such that the actual translation vector is obtained. Experiments have been conducted to verify the effectiveness of our proposed method, and the results indicate a high degree of accuracy.

“Fast registration methodology for fastener assembly of large-scale structure,” IEEE Trans Industrial Electronics (2017)

[86] J. Xu, R. Chen, H. Chen, S. Zhang, and K. Chen, " Fast registration methodology for fastener assembly of large-scale structure," IEEE Trans Industrial Electronics, 64(1),  717-726 (2017); doi:10.1109/TIE.2016.2599140

Abstract

Fastener assembly is a tedious and time-consuming work because operators have to check assembly manuals and find right fastener for each hole. Hence, this article aims to develop a 3D projection system which projects assembly instruction onto the work piece surface directly to guide operators to assemble. However, in order to project the instruction accurately, the corresponding part of the CAD model of the physical scanned area needs to be attained through the rapid and accurate registration. In order to achieve this goal,firstly, a high-accuracy and rapid 3D measurement system is developed; secondly, a fast registration method based on local multi-scale geometric feature vector is proposed to accelerate the registration speed and improve the registration reliability. Experimental results demonstrate the measurement accuracy of the developed system, and verify the feasibility of the proposed registration method. Hence the proposed method can lead to improved assembly efficiency and decreased error probability, making great contributions to large-scale structure assembly.

"High quality 3D shape measurement using saturated fringe patterns,'' Opt. Laser Eng. (2016)

[81] B. Chen and S. Zhang, "High quality 3D shape measurement using saturated fringe patterns,'' Opt. Laser Eng. (2016) (doi:10.1016/j.optlaseng.2016.04.012)

Abstract

This paper proposes a method to potentially conquer one of the challenges in the optical metrology community: optically measuring three-dimensional (3D) objects with high surface contrast. We discover that  for digitally equally phase-shifted fringe patterns, if the fringe period P is an even number, the N = P/2 x k, (k = 1, 2, 3, ...) step algorithm can accurately recover phase even if the fringe patterns are saturated; and if P is an odd number, N = P x k step algorithm can also accurately recover phase even if the fringe patterns are saturated.  This finding leads to a novel method to optically measure shiny surfaces, where the saturation due to surface shininess could be substantially alleviated. Both simulations and experiments successfully verified the proposed method.

"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.

"Flexible real-time natural 2D color and 3D shape measurement," Opt. Express, 2013;

P. Ou, B. Li*, Y. Wang*, and S. Zhang, "Flexible real-time natural 2D color and 3D shape measurement," Opt. Express,21(14), 16736-16741, 2013; doi: 10.1364/OE.21.016736

The majority of existing real-time 3D shape measurement systems only generate non-nature texture (i.e., having illumination other than ambient lights) that induces shadow related issues. This paper presents a method that can simultaneously capture natural 2D color texture and 3D shape in real time. Specifically, we use an infrared fringe projection system to acquire 3D shapes, and a secondary color camera to simultaneously capture 2D color images of the object. Finally, we develop a flexible and simple calibration technique to determine the mapping between the 2D color image and the 3D geometry. Experimental results demonstrate the success of the proposed technique.  

"Mapping cardiac surface mechanics with structured light imaging," American Journal of Physiology: Heart and Circular Physiology, (2012)

J. I. Laughner, S. Zhang, H. Li, C. C. Shao, and I. R. Efimov, "Mapping cardiac surface mechanics with structured light imaging," American Journal of Physiology: Heart and Circular Physiology 303(6), H712-H720, 2012 (Image of the week of October 1, 2012, American Journal of Physiology); doi: 10.1152/ajpheart.00269.2012

Cardiovascular disease often manifests as a combination of pathological electrical and structural heart remodeling. The relationship between mechanics and electrophysiology is crucial to our understanding of mechanisms of cardiac arrhythmias and the treatment of cardiac disease. While several technologies exist for describing whole heart electrophysiology, studies of cardiac mechanics are often limited to rhythmic patterns or small sections of tissue. Here, we present a comprehensive system based on ultrafast three-dimensional (3-D) structured light imaging to map surface dynamics of whole heart cardiac motion. Additionally, we introduce a novel nonrigid motion-tracking algorithm based on an isometry-maximizing optimization framework that forms correspondences between consecutive 3-D frames without the use of any fiducial markers. By combining our 3-D imaging system with nonrigid surface registration, we are able to measure cardiac surface mechanics at unprecedented spatial and temporal resolution. In conclusion, we demonstrate accurate cardiac deformation at over 200,000 surface points of a rabbit heart recorded at 200 frames/s and validate our results on highly contrasting heart motions during normal sinus rhythm, ventricular pacing, and ventricular fibrillation.