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In this work, a statistical model is constructed to forecast the possibility of lung nodules that may grow in the future. This study segments all potential lung nodule candidates using the Multi-scale 3D UNet (M-3D-UNet) method. 34 patients' CT scan series yielded an average of approximately 600 nodule candidates larger than 3 mm, which were then segmented. After removing the arteries, non-nodules and 3D shape variation analysis, 34 actual nodules remained. On actual nodules, the nodule growth Rate (NGR) was calculated in terms of 3D-volume change. Three of the 34 actual nodules had RNG values greater than one, indicating that they were malignant. Compactness, Tissue deficit, Tissue excess, Isotropic Factor and Edge gradient were used to develop the nodule growth predictive measure. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) dynamic image analysis (DIA) is gaining acceptance in geotechnical engineering research. Three-dimensional (3D) DIA extracts features from 8–12 projections of a particle and thus it is believed to verge on the true particle morphology. DIA is fast, efficient and convenient for characterising thousands of particles quickly; nevertheless, it captures shapes that are fundamentally different from the 3D morphologies reconstructed using micro-computed tomography (μCT). In DIA, particle features are interpreted using external images of a particle, which fail to account for differences in imaging perspectives. In addition, 2D and 3D shape descriptors are influenced by differences in dimensionality projection owing to variations in definition, dimensionality and perspectives of the particle images employed, which causes them to differ from their 3D counterparts. In this study, the sand particle size and shape descriptors obtained using both DIA and μCT are compared for three natural sands having wide granulometries. Three-dimensional DIA offers significant advantages in terms of efficiency, while providing adequate representation of Feret dimensions, sphericity and convexity. However, the study demonstrates that 3D roundness is difficult to characterise using DIA and that shape measurements of complex irregular calcareous sands obtained from 3D DIA are not comparable to those obtained using μCT. [ABSTRACT FROM AUTHOR]

To study the compressive properties of an elastomeric porous cylinder, a 360° 3D digital image correlation (DIC) system is proposed. This compact vibration isolation table system captures different segments of the object from four different angles and fields of view, enabling a comprehensive measurement of the full surface of the object. To increase the stitching quality, a coarse–fine coordinate matching method is presented. First, a three-dimensional rigid body calibration auxiliary block is employed to track motion trajectory, which enables preliminary matching of four 3D DIC sub-systems. Subsequently, scattered speckle information characteristics guide fine matching. The accuracy of the 360° 3D DIC system is verified through a three-dimensional shape measurement conducted on a cylindrical shell, and the maximum relative error of the shell's diameter is 0.52%. A thorough investigation of the 3D compressive displacements and strains exerted on the full surface of an elastomeric porous cylinder are investigated. The results demonstrate the robustness of the proposed 360° measuring system on calculating images with voids and indicate a negative Poisson's ratio of periodically cylindrical porous structures. [ABSTRACT FROM AUTHOR]

In three-dimensional (3D) shape measurement based on fringe projection, various factors can degrade the quality of the point cloud. Existing point cloud filtering methods involve analyzing the geometric relationship between 3D space and point cloud, which poses challenges such as complex calculation and low efficiency. To improve the accuracy and speed of point cloud filtering, this paper proposes a new point cloud filtering method based on image segmentation and the absolute phase for the 3D imaging obtained by fringe projection. Firstly, a two-dimensional (2D) point cloud mapping image is established based on the 3D point cloud obtained from fringe projection. Secondly, threshold segmentation and region growing methods are used to segment the 2D point cloud mapping image, followed by recording and removal of the segmented noise region. Using the relationship between the noise point cloud and the absolute phase noise point in fringe projection, a reference noise-free point is established, and the absolute phase line segment is restored to obtain the absolute phase of the noise-free point. Finally, a new 2D point cloud mapping image is reconstructed in 3D space to obtain a point cloud with noise removed. Experimental results show that the point cloud denoising accuracy calculated by this method can reach up to 99.974%, and the running time is 0.954 s. The proposed method can effectively remove point cloud noise and avoid complex calculations in 3D space. This method can not only remove the noise of the 3D point cloud but also can restore the partly removed noise point cloud into a noise-free 3D point cloud, which can improve the accuracy of the 3D point cloud. [ABSTRACT FROM AUTHOR]

The goal of seeking advanced solutions to the descriptions of particle shape, packing and tomographic measurement were key areas promoted by Professor Reg Davies. In this paper we review and reflect on the revolution that has taken place over the last 30 years in our ability to describe and measure particle shape going beyond simple shape factors to their real morphologies of complex particles and particulate assemblies. The paper presents a comprehensive review of how shape has been described and some critical analyses in the form of extended tabulations. We show how digital approaches to particle descriptions can be used to predict the properties of particles and assemblies and their use in simulations of particle processing. We note the current status and prospects for the continued development of microtomographic systems to enable the measurement of particle shape in 3D and also the 3D imaging of complex particulate structures to enable property and processing predictions. Examples of these developments and critical appraisal of their utility will be given. • Collection of evidence for why and how particle shape matters. • Review of how shape description and measurement have changed in the past 30 years. • Review of shape embracing computer models for particulates. • Review of how AI has helped and speculation of how AI can help in the future. [ABSTRACT FROM AUTHOR]

Background: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Objective: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Method: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Results: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects.Conclusions: the development of additive manufacturing technologies (3D printing) has made it possible to manufacture complex structures such as architected materials. However, traditional inspection methods are not suited to these materials, which require volume inspection to examine their internal structure.the aim is to provide a 3D shape measurement method based on the initial computer-aided design (CAD) model used for 3D printing and X-ray radiographs.the CAD model is deformed until its virtual radiographs obtained by simulating the absorption of X-rays through the solid register with experimental radiographs. This registration is achieved by minimising a cost function with respect to the position of control points using radial basis function interpolation.the method’s performance is first evaluated using synthetic data. Its robustness is assessed with respect to image resolution, number of radiographs and noise level. Subsequently, the geometry of a solid with a tetrahedral architecture was quantified by means of a mere five radiographs. Global variation in shape and local defects in lattice structure can be detected.the method enables the in-volume shape of architected materials to be checked without reconstructing the 3D computed tomography volume, but from just a few radiographs. It is robust and can detect local defects. [ABSTRACT FROM AUTHOR]

In 3D printing, as in other manufacturing processes, there is a push for zero-defect manufacturing, mainly to avoid waste. To evaluate the quality of the printed parts during the printing process, an accurate 3D measurement method is required. By scanning the part during the buildup, potential nonconformities to tolerances can be detected early on and the printing process could be adjusted to avoid scrapping the part. Out of many, shape-from-focus, is an accurate method for recovering 3D shapes from objects. However, the state-of-the-art implementation of the method requires the object to be stationary during a measurement. This does not reconcile with the nature of 3D printing, where continuous motion is required for the manufacturing process. This research presents a novel methodology that allows shape-from-focus to be used in a continuous scanning motion, thus making it possible to apply it to the 3D manufacturing process. By controlling the camera trigger and a tunable lens with synchronous signals, a stack of images can be created while the camera or the object is in motion. These images can be re-aligned and then used to create a 3D depth image. The impact on the quality of the 3D measurement was tested by analytically comparing the quality of a scan using the traditional stationary method and of the proposed method to a known reference. The results demonstrate a 1.22% degradation in the measurement error. [ABSTRACT FROM AUTHOR]

Recently it became increasingly evident that the statistical distributions of size and shape descriptors of sedimentary particles reveal crucial information on their evolution and may even carry the fingerprints of their provenance as fragments. However, to unlock this trove of information, measurement of traditional geophysical shape descriptors (mostly detectable on 2D projections) is not sufficient; fully spherical 3D imaging and mathematical algorithms suitable to extract new types of inherently 3D shape descriptors are necessary. Available 3D imaging technologies force users to choose either speed or full sphericity. Only partial morphological information can be extracted in the absence of the latter (e.g., LIDAR imaging). In the case of fully spherical imaging, speed was proved to be prohibitive for obtaining meaningful statistical samples, and inherently 3D shape descriptors were not extracted. Here we present a new method by complementing a commercial, portable 3D scanner with simple hardware to quickly obtain fully spherical 3D datasets from large collections of sedimentary particles. We also present software for the automated extraction of 3D shapes and automated measurement of inherently 3D-shape properties. This technique allows for examining large samples without the need for transportation or storage of the samples, and it may also facilitate the collaboration of geographically distant research groups. We validated our software on a large sample of pebbles by comparing previously hand-measured parameters with the results of automated shape analysis. We also tested our hardware and software tools on a large pebble sample in Kawakawa Bay, New Zealand. [ABSTRACT FROM AUTHOR]

This article compares measurements of particle shape parameters from three-dimensional (3D) X-ray micro-computed tomography (μCT) and two-dimensional (2D) dynamic image analysis (DIA) from the optical microscopy of a coastal bioclastic calcareous sand from Western Australia. This biogenic sand from a high energy environment consists largely of the shells and tests of marine organisms and their clasts. A significant difference was observed between the two imaging techniques for measurements of aspect ratio, convexity, and sphericity. Measured values of aspect ratio, sphericity, and convexity are larger in 2D than in 3D. Correlation analysis indicates that sphericity is correlated with convexity in both 2D and 3D. These results are attributed to inherent limitations of DIA when applied to platy sand grains and to the shape being, in part, dependent on the biology of the grain rather than a purely random clastic process, like typical siliceous sands. The statistical data has also been fitted to Johnson Bounded Distribution for the ease of future use. Overall, this research demonstrates the need for high-quality 3D microscopy when conducting a micromechanical analysis of biogenic calcareous sands. [ABSTRACT FROM AUTHOR]

• An accurate calibration method for fringe projection vision sensor based on vanishing-constraints is proposed. • Precise coordinate correspondence is established between camera and projector images. • Significant calibration errors or potential failure, traditionally caused by correspondence mismatches between image points and 3D points of the planar calibration target, are effectively mitigated. In fringe projection profilometry (FPP), calibration of the vision sensor is crucial to ensure the accuracy of three-dimensional (3D) shape measurement. However, due to correspondence errors of planar calibration target (PCT) 3D points and its image points, and low mapping accuracy between projector pixels and camera pixels, traditional calibration methods based on the PCT sometimes cannot provide reliable and accurate results. Aiming at these problems, a high-accuracy calibration method based on vanishing constraints for fringe projection vision sensor (FPVS) is proposed in this paper. The intrinsic parameters are calibrated using the constraints of vanishing points, the rotation matrix is calibrated using the constraints of vanishing lines, and the optimal calibration parameters are estimated by the objective function established based on the 2D and 3D constraints of feature points. Experimental results demonstrated the performance of our calibration method. [ABSTRACT FROM AUTHOR]

Effective prosthetic socket design following lower limb amputation depends upon the accurate characterization of the shape of the residual limb as well as its volume and shape fluctuations. Objective: This study proposes a novel framework for the measurement and analysis of residual limb shape and deformation, using a high-resolution and low-cost system. Methods: A multi-camera system was designed to capture sets of simultaneous images of the entire residuum surface. The images were analyzed using a specially developed open-source three-dimensional digital image correlation (3D-DIC) toolbox, to obtain the accurate time-varying shapes as well as the full-field deformation and strain maps on the residuum skin surface. Measurements on a transtibial amputee residuum were obtained during knee flexions, muscle contractions, and swelling upon socket removal. Results: It was demonstrated that 3D-DIC can be employed to quantify with high resolution time-varying residuum shapes, deformations, and strains. Additionally, the enclosed volumes and cross-sectional areas were computed and analyzed. Conclusion: This novel low-cost framework provides a promising solution for the in vivo evaluation of residuum shapes and strains, as well as has the potential for characterizing the mechanical properties of the underlying soft tissues. Significance: These data may be used to inform data-driven computational algorithms for the design of prosthetic sockets, as well as of other wearable technologies mechanically interfacing with the skin. [ABSTRACT FROM AUTHOR]

Highlights • We present a behavometrics method via a 3D dynamic face speaking a private passcode. • We establish the first public speech-driven 3D dynamic face dataset S3DFM. • The 3D speaking face features are repeatable and distinctive for behavometrics. • The method is robust against spoofing and head pose variations. • The method is applicable to any passcode and is invariant to speaking speed. Abstract Face biometrics have achieved remarkable performance over the past decades, but unexpected spoofing of the static faces poses a threat to information security. There is an increasing demand for stable and discriminative biological modalities which are hard to be mimicked and deceived. Speech-driven 3D facial motion is a distinctive and measurable behavior-signature that is promising for biometrics. In this paper, we propose a novel 3D behaviometrics framework based on a "3D visual passcode" derived from speech-driven 3D facial dynamics. The 3D facial dynamics are jointly represented by 3D-keypoint-based measurements and 3D shape patch features, extracted from both static and speech-driven dynamic regions. An ensemble of subject-specific classifiers are then trained over selected discriminative features, which allows for a discriminant speech-driven 3D facial dynamics representation. We construct the first publicly available Speech-driven 3D Facial Motion dataset (S3DFM) that includes 2D-3D face video plus audio samples from 77 participants. The experimental results on the S3DFM show that the proposed pipeline achieves a face identification rate of 96.1%. Detailed discussions are presented, concerning anti-spoofing, head pose variation, video frame rate, and applicability cases. We also give comparison with other baselines on "deep" and "shallow" 2D face features. [ABSTRACT FROM AUTHOR]

Highlights • A segmented quantization phase coding and decoding method is proposed. • A new phase unwrapping algorithm based on segmented quantization phase coding is proposed. • The proposed method can guarantee high measurement accuracy in high-frequency. • The proposed method allows the measurement of both single object and isolated objects with complicated shape because of using segmented quantization phase coding method. • The proposed method only needs six patterns to obtain absolute phase, the model has advantages for high-speed measurement applications. Abstract Codeword is very important in phase unwrapping based on phase coding method. Each phase coding fringe is marked with a unique codeword and then used to determine the fringe order for absolute phase retrieval. However, the traditional phase coding method is limited by the number of codeword. To overcome this problem, a segmented quantization phase coding and decoding method is proposed to achieve absolute phase retrieval without reducing the difference between adjacent quantized phase values or increasing the quantization levels. The quantized phase is modulated by a specific coding sequence and then embedded into phase coding fringe patterns, thereby greatly improving the accuracy of the decoding. The coding creates multiple segments of the whole region and each segment embeds the special coding sequence. Through the corresponding decoding algorithm, the fringe order can be obtained, and following this, the absolute phase is obtained. Simulation and experimental results demonstrate the feasibility and superiority of the proposed method to measure both a single object and multiple isolated objects. [ABSTRACT FROM AUTHOR]

We present an adaptive phase unwrapping method based on geometric constraints and the gradient field without additional images for high-speed three-dimensional (3D) shape measurement. Specifically, we reconstruct the 3D geometry of moving objects frame by frame. We first create a reference phase map at the depth provided by the former frame. Then we optimize the depth value by validating the continuity of the computed unwrapped phase based on the modulus of the gradient field and recalculate the correct absolute phase map with the optimal depth value. After reconstructing the 3D geometry of the current frame, 3D data are delivered to the next frame. In particular, a geometric constraint-based method is applied in the first frame. Experiment results indicate that our approach, which requires only three phase-shifted fringe patterns per frame, can measure moving objects with high accuracy and robustness. Additionally, several isolated objects can also be measured by our method if they are continuous. [ABSTRACT FROM AUTHOR]

This paper proposes a method of generating 3D building models with precise geospatial information and a photograph-based façade appearance from panoramic image sequences and digital maps. 3D building modeling research is actively being conducted in areas such as geographic information systems, virtual reality, and augmented reality. However, the generation of realistic 3D models from a ground-level viewpoint is still extremely costly in terms of labor of modeling experts, and collection of data. We have developed a method for 3D building modeling with high-resolution photograph-based appearance information using panoramic images captured at ground level with a mobile mapping system, and geospatial information obtained from a digital map. The proposed method includes 1) pre-processing for tilt correction and base 3D model generation, 2) geo-registration of panoramic images with minimal user input, and 3) building height and shape estimation. This paper presents the proposed method and the quantitative performance measure obtained from a developed test modeling system. In addition, modeling results from an experimental dataset are also presented. [ABSTRACT FROM AUTHOR]

Mach-Zehnder interferometer based sensors for simultaneous distance and velocity measurement allow for absolute 3-D shape measurements of rotating workpieces for instance in cutting lathes. The achievable shape uncertainty is limited to around one micron due to the speckle effect and temperature drifts, however. In this paper, a laser Doppler distance sensor with phase evaluation (P-LDD sensor) with a camera based scattered light detection is investigated. A novel speckle separation technique and in-situ fringe distance calibration method are realized to reduce the measurement uncertainty. A coherent fiber bundle is employed to forward the scattered light towards the camera. This enables a compact and passive sensor head with keyhole access. Compared with a photo detector based sensor, the camera based setup allows to decrease the measurement uncertainty by the order of one magnitude. As a result, the total shape uncertainty of absolute 3-D shape measurements can be reduced to about 100 nm. [ABSTRACT FROM AUTHOR]

The number of global mechanical equilibria as a shape descriptor (among others, for sedimentary particles) is at the forefront of current geophysical research. Although the technology is already available to provide scanned, 3D images of the particles (appearing as fine spatial discretization of smooth surfaces), nevertheless, the automated identification and measurement of global equilibria on such 3D images has not been solved so far. The main difficulty lies in the algorithmic distinction between local equilibria (associated with the small un-evenness of the pebble's surface) and global equilibria, associated with the overall shape. The former are easily measured, however, only the latter provide meaningful physical information. Here we provide and illustrate an algorithm to detect global equilibrium points on a finely discretized, polyhedral surface provided by 3D scan of sedimentary particles. [ABSTRACT FROM AUTHOR]

In the existing intensity-ratio measuring methods, unwrapping the intensity ratio may be erroneous or even fail when measuring complex and isolated objects. This paper presents an improved three-dimensional (3-D) profile measuring method based on intensity-ratio measurement. Two shifting triangular patterns are projected to generate a triangular intensity-ratio distribution, and a Ronchi grating is projected to correctly divide the triangular intensity-ratio regions. Then, an absolute intensity ratio is retrieved point-by-point with the periodic label of the projected Ronchi grating. Finally, the intensity-ratio-to-height mapping algorithm is used to reconstruct the 3-D surface shape. The experimental results have demonstrated the feasibility and validity of the proposed method in restoring 3-D surface shape of the complex and isolated objects. [ABSTRACT FROM AUTHOR]

Existing methods to measure 3D shape of complex object involve processing more than six captured images to obtain the absolute phase, which limit the measurement speed. This paper presents two sinusoidal fringes and two triangular wave fringes which is used to measure 3D shape of complex object. The two-step phase-shifting sinusoidal fringes and two-step phase-shifting triangular wave fringes are calculated to obtain the wrapped phase, and then the two-step phase-shifting triangular wave fringes are used to determine the fringe order. Due to decrease the number of projection fringes, the speed of measurement increases. The triangular wave fringe carries more information of the object than linear increasing/decreasing ramp fringe in the actual measurement, more noise in the base phase to be overcome, thus improving the measurement accuracy. The benefits can be widely applied in high-speed, real-time 3D measurement of complex shape. Experimental results have demonstrated that the proposed method is simple, but effective. [ABSTRACT FROM AUTHOR]

There have been active studies on optimized dithering techniques to improve 3D shape measurement quality with defocused projectors. These techniques optimize the fringe quality in either phase domain or intensity domain according to their objective functions. Phase based optimization is direct and effective, but is sensitive to projector defocus levels. Intensity based optimization is robust to projector defocus levels, but it does not fully improve the phase quality. This paper presents a joint optimization technique to combine the merits of both the intensity and phase based optimization, which includes a pre-intensity optimization and a further optimization based on the synthesized error function. Then this technique is implemented in two frameworks, the whole-fringe optimization and the best-patch optimization, to generate binary fringe patterns. Both simulations and experiments show that the proposed technique can generate binary fringe patterns with high phase quality and robustness to projector defocus levels. [ABSTRACT FROM AUTHOR]

Fringe projection profilometry is a popular optical method for three-dimensional (3-D) shape measurement because of its high accuracy, fast measurement speed, and full-field inspection nature. However, due to the limited dynamic range of the digital camera, saturated pixels in the captured images will lead to serious phase errors and measurement errors when the measured object has a drastic texture variation. To deal with such a problem, an adaptive digital fringe projection technique for high dynamic 3-D shape measurement is proposed. In this method, phase-shifting fringes are adaptively generated with the aid of a coordinates mapping process and binary-search technique to eliminate saturation. Compared with previous adaptive fringe projection techniques, the camera response function and homographic mapping between the camera and projector are not needed, making the whole measurement easier to carry out and less laborious. Experiments validate the effectiveness and superiority of the proposed method for high-dynamic range 3-D shape measurement. [ABSTRACT FROM AUTHOR]

In the last decade, a significant number of techniques for three-dimensional (3D) shape measurement have been proposed. There are a large number of measurement demands for metallic workpieces with shiny surfaces in industrial applications; however, such shiny surfaces cannot be directly measured using the conventional structured light method. Therefore, various techniques have been investigated to solve this problem over the last few years. Some reviews summarize the different 3D imaging techniques; however, no comprehensive review exists that provides an insight into high-dynamic range (HDR) 3D shape measurement techniques used for shiny surfaces. We present a survey of recent HDR techniques for the digitization of shiny surfaces and classify and discuss the advantages and drawbacks of different techniques with respect to each other. [ABSTRACT FROM AUTHOR]

Conventional methods based on analyses of the absolute gray levels of pixels in fringe pattern images are affected by the problems of image saturation, interreflection, and high sensitivity to noise when obtaining three-dimensional (3D) shape measurements of shiny surfaces. This study presents a robust, adaptive, and fast 3D shape measurement technique, which adaptively adjusts the pixel-wise intensity of the projected patterns, thus it avoids image saturation and has a high signal to noise ratio (SNR) during 3D shape measurement for shiny surfaces. Compared with previous time-consuming methods using multiple exposures and the projection of fringe patterns with multiple intensities, where a large number of fringe pattern images need to be captured, the proposed technique needs to capture far fewer pattern images for measurement. In addition, it can greatly reduce the time costs to obtain the optimal projection intensities by the fusion of uniform gray level patterns and coordinates mapping. Our experimental results demonstrate that the proposed technique can achieve highly accurate and efficient 3D shape measurement for shiny surfaces. [ABSTRACT FROM AUTHOR]

This paper presents a novel fringe projection technique for fast three-dimensional (3-D) shape measurements of moving highly reflective objects. By combining the standard three-step phase-shifting fringe patterns with a digital speckle image, dynamic 3-D reconstructions of shiny surfaces can be efficiently achieved with only four projected patterns. The phase measurement is performed by three-step phase-shifting algorithm as it uses the theoretical minimum number of fringe patterns for phase-shifting profilometry. To avoid the camera saturation, a dual-camera fringe projection system is built to measure shiny objects from two different directions. The erroneous phase obtained from a saturated pixel is corrected by the phase of its corresponding pixel in the other view which is free from the saturation problem. To achieve high measurement accuracy, the corresponding high light intensity areas in cameras are found by sub-pixel matches of the speckle pattern in either view. Benefited from the trifocal tensor constraint, the corresponding points in the two wrapped phase maps can be directly established, and thus, the difficulties in determining the correct fringe order for the discontinuous or isolated surfaces can be effectively bypassed. Experimental results indicate that the proposed method is able to successfully measure highly reflective surfaces for both stationary and dynamic scenes. [ABSTRACT FROM AUTHOR]

• Strong interreflections in 3D shape measurement are overcome, and direct illumination is distinguished from global illumination. • Efficient 3D shape measurement in the presence of strong interreflections is achieved, with 94% measurements saved. • Deep-learning is utilized for accurate reconstruction. • Sampling Fourier strategy is utilized to reduce measurements. Strong interreflections cause intractable systematic errors to traditional 3D shaping methods, for example, fringe projection profilometry. Parallel single-pixel imaging (PSI) captures the light transport coefficients between the camera projector pair, thus overcoming the influence of interreflections. However, PSI requires a large number of measurements, causing poor capturing efficiency. To achieve efficient 3D shape measurement in the presence of strong interreflections, we present a deep-learning-based parallel single-pixel imaging method (dlPSI), featuring adopting a deep-learning network to achieve accurate light transport coefficient reconstruction and using sampling Fourier strategy to reduce measurements. The deep-learning network is designed to suppress the noise caused by undersampling the Fourier domains. Experiments prove that our dlPSI with the characteristic-based deterministic Fourier sampling strategy achieves high-quality 3D shape measurement while saving 94% of measurements. [ABSTRACT FROM AUTHOR]

This paper reviews high-speed optical 3D sensing technologies for obtaining the 3D shape of a target using a camera. The focusing speed is from 100 to 1000 fps, exceeding normal camera frame rates, which are typically 30 fps. In particular, contactless, active, and real-time systems are introduced. Also, three example applications of this type of sensing technology are introduced, including surface reconstruction from time-sequential depth images, high-speed 3D user interaction, and high-speed digital archiving. [ABSTRACT FROM AUTHOR]

Recovering the three dimensional structure of a scene accurately and robustly is important for object modelling and robotic grasp planning, which in turn are essential prerequisites for grasping unknown objects in a cluttered environment. Shape recovery techniques are broadly described as either passive or active. Passive methods include recovering shape from a single image using cues such as shading, texture or focus, and shape from multiple views using stereopsis or structure-from-motion. Passive shape recovery has relatively low power requirements, is non-destructive and more akin to our biological sensing modalities. However, the accuracy and reliability of passive techniques is critically dependent on the presence of sufficient image fea tures and the absence of distractions such as reflections. [ABSTRACT FROM AUTHOR]

Binary pattern defocused projection method can overcome the nonlinear gamma of the projector, as well as filter high harmonics and high-frequency noise. However, high-accuracy three-dimensional (3-D) shape measurement of complex surface using it still remains a challenge. Therefore, a novel Gray code plus phase-shifting method based on defocusing is proposed to solve the problem. The edges of Gray code patterns become blurred owing to defocus, which makes the recovery of accurate Gray code patterns difficult. To solve this problem, the positive and inverse Gray code patterns are projected to obtain threshold values, which are used to achieve the binarization of Gray code patterns. This method is robust and suitable for different defocus levels. Compared with the traditional Gray code plus phase-shifting method, the experimental results prove the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

An improved two-step phase-shifting profilometry is put forward in three-dimensional (3D) shape measurement. Firstly, two phase-shifted randomly sinusoidal fringe patterns are projected onto the tested object by digital-light-processing (DLP) projector. The fringe patterns modulated with the object's surface are captured by a CCD camera. Secondly, the background and modulation components are obtained by parameter estimation using the least square method; fringe normalization is accomplished by the background bias removal and modulation normalization of a given deformed fringe. Then based on the statics characteristics of fringe gray, the phase step between two phase-shifted randomly sinusoidal fringe patterns is determined by using the inverse cosine function. Then, the phase is extracted from the two frame's normalized patterns and the step value. Finally, the experimental evaluation is conducted to prove the validity and performance of the proposed method. The experimental result is analyzed and compared with that of the method by reference 16. The effectiveness and superiority of the proposed method has been demonstrated. [ABSTRACT FROM AUTHOR]

View-based 3D shape retrieval is a popular branch in 3D shape analysis owing to the high discriminative property of 2D views. However, many previous works do not scale up to large 3D shape databases. We propose a two layer coding (TLC) framework to conduct shape matching much more efficiently. The first layer coding is applied to pairs of views represented as depth images. The spatial relationship of each view pair is captured with so-called eigen-angle, which is the planar angle between the two views measured at the center of the 3D shape. Prior to the second layer coding, the view pairs are divided into subsets according to their eigen-angles. Consequently, view pairs that differ significantly in their eigen-angles are encoded with different codewords, which implies that spatial arrangement of views is preserved in the second layer coding. The final feature vector of a 3D shape is the concatenation of all the encoded features from different subsets, which is used for efficient indexing directly. TLC is not limited to encode the local features from 2D views, but can be also applied to encoding 3D features. Exhaustive experimental results confirm that TLC achieves state-of-the-art performance in both retrieval accuracy and efficiency. [ABSTRACT FROM PUBLISHER]

Binary fringe defocused projection is a promising method for high-speed, high-accuracy three-dimensional (3D) shape measurement because of the advantages of superfast projection and capability to overcome the nonlinear gamma of the projector. However, the application of this approach for complex surface measurement remains a challenge. Thus, a method that combines binary fringe and phase coding fringe based on defocusing is proposed to achieve fast-speed, high-accuracy 3D shape measurement of complex surfaces. However, in the case of defocusing, as the number of phase coding fringe cycles increases, the fringe orderk(x,y) becomes difficult to judge, errors occur in the jump area, and the periodic dislocation problem becomes worse, ultimately leading to phase unwrapping error. A phase-shifting coding method is thus presented to resolve these issues. This method not only alleviates the difficulty in judging the fringe order as a result of defocusing but also resolves the correction problem, and in turn, the periodic dislocation problem. Thus, measurement accuracy is improved. Experimental results demonstrate the feasibility and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

Projector nonlinearity is a common problem for digital structured light-based three-dimensional (3-D) shape measurement techniques. A temporal-spatial binary encoding method is presented for the purpose of eluding it. We build a 3-D shape measurement scheme by combining our proposed method with phase measurement profiling. A standard sinusoidal fringe pattern is divided into more than two binary fringe patterns using specially designed temporal and spatial binary encoding rule based on intensity hierarchic quantification, and then are in-focus projected onto the measured object at a time sequence to reconstruct a frame phase-shifting fringe image. On account of the projected binary fringe pattern strictly consisting of zeros and ones, the influence of the projector nonlinearity on the measurement result can be effectively ruled out and simultaneously enables high-quality sinusoidality. In-depth investigations by theoretical analysis and experiments are conducted to demonstrate the performance of this method. [ABSTRACT FROM AUTHOR]

The recently proposed optimized dithering techniques are able to improve measurement quality obviously. However, those phase-based optimization methods are sensitive to the amount of defocusing while intensity-based optimization methods cannot reduce the phase error efficiently. This paper presents a novel method, minimizing a proposed objective function named intensity residual error (IRE), as well as a novel framework, optimizing pixels group by group, to construct binary patterns for high-quality 3D shape measurement. Both the simulation and experimental results show that this proposed algorithm can achieve phase quality improvements over other recently optimized dithering techniques with various amounts of defocusing. [ABSTRACT FROM AUTHOR]

Digital Image Correlation is widely used for shape, motion and deformation measurements. Basically, the main steps of 3D-DIC for shape measurement applications are: off-line camera calibration, image matching and triangulation. The matching of each pixel of an image to a pixel in another image uses a so-called subset (correlation window). Subset size selection is a tricky issue and is a trade-off between a good spatial resolution, achieved with small subsets that preserve image details, and a low displacement uncertainty achieved with large subsets that can smooth image details. In this paper, we present a new multi-step DIC algorithm specially designed for measuring the 3D shape of objects with sharp edges. With this new algorithm an accurate 3D reconstruction of the whole object, including sharp edges that are preserved, can be achieved. [ABSTRACT FROM AUTHOR]

The multiview phase-shifting method shows its powerful capability in achieving high resolution threedimensional (3-D) shape measurement. Unfortunately, this ability results in very high computation costs and 3-D computations have to be processed offline. To realize real-time 3-D shape measurement, a hybrid parallel computing architecture is proposed for multiview phase shifting. In this architecture, the central processing unit can co-operate with the graphic processing unit (GPU) to achieve hybrid parallel computing. The high computation cost procedures, including lens distortion rectification, phase computation, correspondence, and 3-D reconstruction, are implemented in GPU, and a three-layer kernel function model is designed to simultaneously realize coarse-grained and fine-grained paralleling computing. Experimental results verify that the developed system can perform 50 fps (frame per second) real-time 3-D measurement with 260 K 3-D points per frame. A speedup of up to 180 times is obtained for the performance of the proposed technique using a NVIDIA GT560Ti graphics card rather than a sequential C in a 3.4 GHZ Inter Core i7 3770. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three-dimensional (3-D) measurement systems based on coded-light techniques are conventionally limited by the projection speed, which is typically in the range of a few 100 Hz, resulting in 3-D frame rates of 1 to 60 Hz. We propose to use an array projector for 3-D shape measurements, which enables much higher projection frame rates of up to the 100-kHz range. In contrast to previous setups, it does not project well-known phase-shifted sinusoidal fringes and Gray code patterns, but aperiodic sinusoidal fringes. This new technique, based on sine-shaped fringes with spatially and temporally varying offset, amplitude, period length, and phase shift, allows accurate 3-D measurement of objects, even with sharp edges, high slope, or varying surface properties, at high speed up to the kilohertz range. This paper explains the 3-D measurement principle and the basic design of an array projector that projects aperiodic sinusoidal fringes. It verifies the consistency between specified and projected patterns and points out the results of the setup's characterization, e.g., of its high-speed capability. Furthermore, first 3-D shape measurements at a projection frame rate of 3 kHz resulting in a 3-D frame rate of >330 Hz are presented and evaluated. [ABSTRACT FROM AUTHOR]

Phase shifting using digital light processing (DLP) projectors enables high-speed three-dimensional (3-D) shape measurements based on a pattern projection method. However, faster phase shifting is required in industry to reduce the measurement time. For this purpose, it is necessary to precisely control the fringe pattern, but conventional DLP projectors afford limited control of the pattern due to their low-refresh rate (typically 120 Hz). Here, a multiwavelength spatiotemporal phase-shifting technique is proposed for faster 3-D shape measurements using a 3CCD camera. The projector consists of a single micro-electro-mechanical system mirror and three laser diodes of different wavelengths. The intensity modulation is transformed from the time to the spatial domain. The phases of the fringe patterns are independently controlled at each wavelength. Images are simultaneously captured of the projected patterns deformed in accord with the surface profile of the objective. The method is validated using a gray code technique for the height measurement of a sample in large steps. [ABSTRACT FROM AUTHOR]

Statistical patterns have been used for structured illumination within a stereo-photogrammetry setup to precisely measure the shape of nearly arbitrary objects in a short time. This contribution gives an overview of recently developed projection setups based on such statistical patterns. Coherent and incoherent approaches as well as the applied reconstruction algorithm are explained. The results show the suitability of the statistical pattern projection approach to replace the commonly used slow digital light processing (DLP) projectors of threedimensional shape sensors and facilitate measurements in an ultrashort time frame (microsecond range), e.g., to track moving objects. [ABSTRACT FROM AUTHOR]

A new probing and compensation method is proposed to improve the three-dimensional (3D) measuring accuracy of 3D shapes, including irregular surfaces. A new tactile coordinate measuring machine (CMM) probe with a five-degree of freedom (5-DOF) force/moment sensor using carbon fiber plates was developed. The proposed method efficiently removes the anisotropic sensitivity error and decreases the stylus deformation and the actual contact point estimation errors that are major error components of shape measurement using touch probes. The relationship between the measuring force and estimation accuracy of the actual contact point error and stylus deformation error are examined for practical use of the proposed method. The appropriate measuring force condition is presented for the precision measurement. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a high-speed three-dimensional (3-D) shape measurement technique for dynamic scenes by using bi-frequency tripolar pulse-width-modulation (TPWM) fringe projection. Two wrapped phase maps with different wavelengths can be obtained simultaneously by our bi-frequency phase-shifting algorithm. Then the two phase maps are unwrapped using a simple look-up-table based number-theoretical approach. To guarantee the robustness of phase unwrapping as well as the high sinusoidality of projected patterns, TPWM technique is employed to generate ideal fringe patterns with slight defocus. We detailed our technique, including its principle, pattern design, and system setup. Several experiments on dynamic scenes were performed, verifying that our method can achieve a speed of 1250 frames per second for fast, dense, and accurate 3-D measurements. [Copyright &y& Elsevier]

Imbalance suggests a feeling of dynamism and movement in static objects. It is therefore not surprising that many 3D models stand in impossibly balanced configurations. As long as the models remain in a computer this is of no consequence: the laws of physics do not apply. However, fabrication through 3D printing breaks the illusion: printed models topple instead of standing as initially intended. We propose to assist users in producing novel, properly balanced designs by interactively deforming an existing model. We formulate balance optimization as an energy minimization, improving stability by modifying the volume of the object, while preserving its surface details. This takes place during interactive editing: the user cooperates with our optimizer towards the end result. We demonstrate our method on a variety of models. With our technique, users can produce fabricated objects that stand in one or more surprising poses without requiring glue or heavy pedestals. [ABSTRACT FROM AUTHOR]

Three-step phase-shifting is an extensively employed method for three-dimensional (3D) shape measurement, especially for high speed 3D image acquisition. However, since only three fringe images are used, the measurement result is susceptible to sensor and environment noise. In this paper, we propose a third harmonic injection technique for three-step phase-shifting profilometry to reduce the error caused by the uncertainty noise. By adding a measure of third harmonic to the sinusoidal waveform, the amplitude of the sinusoidal foundational component can be increased by 15.5%, which results in the reduction of the phase error caused by random noise. The advantages of the proposed technique lie in its simplicity, insensitivity to image defocus, and applicability for high speed 3D imaging by projector defocus. Theoretical analysis, simulations, and experiments are presented to verify the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

Abstract: An optical measurement system, which is capable of simultaneously measuring surface profile and three-dimensional (3-D) deformation of small objects, has been developed by the combination of fringe projection and a two-dimensional digital image correlation (DIC) technique. In the proposed approach, it requires only one camera and one projector. The surface profile and out-of-plane deformation are determined by fringe projection with the phase-shifting method. The in-plane deformation is determined by comparing the surface texture of specimen before and after deformation with the DIC technique. A simple procedure is described which enables determination of texture image from phase-shifting images. As an application, the developed system was used to investigate the mechanical behavior of molded pulp material in micro-zone during tension testing. [Copyright &y& Elsevier]

A mobile robot equipped with two lasers and a CCD camera for pipe inspection is proposed. Circular laser streaks that appeared on the inner surface of the pipe reveal the shape of the pipe. The 3D shape of a sewer pipe can be reconstructed considering the movement of the mobile robot along the pipe. Since the tilt of the mobile robot with respect to the axis of the pipe appears as the deformation between two circular streaks, the shape of a sewer pipe can be measured accurately, regardless of the tilt of the robot. [ABSTRACT FROM AUTHOR]

Automatically adapting the camera exposure time is crucial for industrial applications where minimum human intervention is usually desirable. However, it is very challenging to realize such a capability for a conventional fringe projection system where only a finite increment of the exposure time is allowed due to its digital fringe generation nature. We study the generation of sinusoidal fringe patterns by properly defocusing binary ones, which permits the use of an arbitrary exposure time. This provides the potential to adapt the exposure time automatically. We present the principle of an automatic exposure technique and show some ex- perimental results. [ABSTRACT FROM AUTHOR]

Quality control is of utmost importance in the metal industry. It requires online measurement and inspection systems which provide precise feedback to closed-loop controllers in industrial facilities. In rolled products, shape is one of the main quality criteria. In this paper, a low-cost real-time 3-D shape measurement system for long flat (FL)-rolled products based on laser triangulation is proposed. The system provides online measurements of two geometrical features of the shape of rolled products: flatness and width. The proposed system is based on 3-D surface reconstruction of rolled products with which flatness can be measured accurately and continuously across the whole width of the strip. Three-dimensional surface reconstruction provides highly accurate width measurements not only of FL products, as do most other systems, but also of non-FL products. The accuracy of the laser extraction method used to reconstruct the surface of the rolled products is evaluated, as well as the online performance of the system. [ABSTRACT FROM PUBLISHER]

In this paper, we propose and evaluate a novel shape measure describing the extent to which a 3D polygon mesh is rectilinear. The rectilinearity measure is based on the maximum ratio of the surface area to the sum of three orthogonal projected areas of the mesh. It has the following desirable properties: 1) the estimated rectilinearity is always a number from (0,1]; 2) the measure is invariant under scale, rotation, and translation; 3) the 3D objects can be either open or closed meshes, and we can also deal with degenerate meshes; 4) the measure is insensitive to noise, stable under small topology errors, and robust against face deletion and mesh simplification. Moreover, a genetic algorithm (GA) can be applied to compute the approximate rectilinearity efficiently. We find that the calculation of rectilinearity can be used to normalize the pose of 3D meshes, and in many cases it performs better than the principal component analysis (PCA) based method. By applying a simple selection criterion, the combination of these two methods results in a new pose normalization algorithm which not only provides a higher successful alignment rate but also corresponds better with intuition. Finally, we carry out several experiments showing that both the rectilinearity based pose normalization preprocessing and the combined signatures, which consist of the rectilinearity measure and other shape descriptors, can significantly improve the performance of 3D shape retrieval. [ABSTRACT FROM AUTHOR]

Abstract: Optical methods that give displacement or strain fields are now widely used in experimental mechanics. Some of the methods can only measure in-plane displacements/strains on planar specimens and some of them can give both in-plane and out-of-plane displacement/strain fields on any kind of specimen (planar or not). In the present paper, the stereovision technique that uses two cameras to measure 3-D displacement/strain fields on any 3-D object is presented. Additionally, a quite inclusive list of references on applications of stereovision (and 3-D DIC) to experimental mechanics is given at the end of the paper. [Copyright &y& Elsevier]

Learning 3D shape representations from structured-light images for 3D reconstructions has become popular in many fields. This paper presents a new approach integrating a fringe-to-phase network with a fringe projection profilometry (FPP) technique to achieve 3D reconstructions with superior accuracy and speed performance. The proposed fringe-to-phase network has a UNet-like architecture, capable of retrieving three wrapped phase maps directly from a color image comprising three fringe patterns with designated frequencies. Because the phase maps contain the 3D shape representations of the measurement target, they serve as an intermediary to transform the single-shot fringe-pattern image into the 3D shapes of the target. The datasets with ground-truth phase labels are generated by using a tri-frequency FPP method. Unlike the existing techniques, the proposed approach yields both high-accuracy and fast-speed 3D reconstructions. Experiments have been accomplished to validate the proposed technique, which provides a promising tool for numerous scientific research and industrial applications. [Display omitted] • Integration of structured-light technique and deep learning. • Learning 3D shape representation from a single fringe image. • Phase is retrieved directly from a single fringe image. • Yielding higher accuracy than other single-shot techniques. • Providing faster speed than existing accurate measurement techniques. [ABSTRACT FROM AUTHOR]