Recently, researchers have found that the power of deep learning can be leveraged to perform high quality 3D shape measurement by directly learning from a single-shot fringe image. However, such end-to-end fringe-to-depth learning has limited flexibility given that its trained deep neural network can only be used for patterns with a certain frequency. This research proposes a phase-to-phase learning approach to address such limitation. By establishing a phase-to-phase training network from phase obtained from Fourier transform to phase obtained from phase shifting, this proposed network can be flexibly applied to measurements with fringe images of different pattern frequencies.
3D imaging sensors are important for intelligent robots to figure out complicated and unknown assembly tasks. To perform a smooth robotic assembly with high precision, it is crucial to incorporate 3D imaging sensors that can scan, recognize, and characterize fine-scale features (e.g., small screws). We developed an integrated robotic 3D vision system based on high-resolution structured light 3D vision based on fringe projection. Our preliminary testing has demonstrated the promise of our integrated system in precision assembly operations supported by the capability of extracting fine-scale key features through high-resolution surface mapping.
Fringe projection (FP) is one of the most widely used method to precisely measure the 3D geometry of complicated surfaces. However, when the object is in motion, it is difficult to estimate the motion or displacement that happens between the frames. The most commonly used method for estimating the in-plane displacement is Digital Image Correlation (DIC). It has been widely used in the area of experimental mechanics. As the traditional DIC method uses a single camera, it is difficult to recover the 3D shape of the object. In this paper, we propose a novel method called digital height correlation method for measuring surface profile deformation. The height data obtained from FP can be used to estimate the deformation. The proposed method involves measuring the 3D profile of an object, which has rich surface topographic variations using a high-accuracy fringe projection method. Then, the 3D profiles obtained from the before and after displacement state are correlated to extract the displacement map. Specifically, the out-of-plane displacement is extracted by applying the correlation technique to the height map obtained from the 3D profile of the object. The accuracy and efficacy of the digital height correlation method are validated using rigid-body translation tests and tensile tests of a rubber specimen. Experiments conducted will demonstrate the success of the proposed method.
Three dimensional (3D) topology data obtained from different optical metrology techniques tend to produce local disagreements which may yield incorrect judgement from inspectors especially under scenarios of precision metrology. This research explores statistical methods to provide a functional scoring for similarities. The investigation is conducted using two statistical methods (Pearsons correlation coefficient and image distance), two optical techniques (structured light and focus variation microscopy) and two application scenarios (metal additive printing and ballistic forensic examination). Experimental results show the promise of using statistical tools to assist binary decisions for matching/non-matching even if 3D topology data are obtained from different optical techniques.
The paper introduces a new method of digital image correlation by making use of the transitioning state of the digital micro-mirror device (DMD). The projector should be given an OFF time in order to introduce flashing light for dynamic imaging. The dark period between DMD’s ON time is used to solve the saturation problem. Multiple captures are made during each projector cycle. The final unsaturated camera image can be obtained by combining all the images captured during that cycle. Experiments conducted demonstrate the success of the proposed method in performing digital image correlation for highly reflective surface.
High-speed and high-accuracy three-dimensional (3D) measurement plays an important role in numerous areas. The recent proposed binary defocusing techniques have enabled the speed breakthrough by utilizing 1-bit binary fringe patterns with the advanced digital light processing (DLP) projection platform. To enhance the phase quality and measurement accuracy, extensive research has also been conducted to modulate and optimize the binary patterns spatially or temporally. However, it remains challenging for such techniques to measure objects with high dynamic range (HDR) of surface reflectivity. Therefore, to overcome this problem, this paper proposes a novel HDR 3D measurement method based on spectral modulation and multispectral imaging. By modulating the illumination light and acquiring the fringe patterns with a multispectral camera, high-contrast HDR fringe imaging and 3D measurement can be achieved. Experiments were carried out to demonstrate the effectiveness of the proposed strategy.
This research proposes a motion-induced error reduction method for phase shifting profilomtry. Particularly, each illuminated fringe pattern will be captured twice in one projection cycle when imaging a highly dynamic scene, resulting in two sets of phase shifted fringe images be obtained. A phase map will be computed for each phase shifting set in preparation for error analysis. Finally, motion-induced phase errors will be compensated by examining the difference of the two phase maps obtained respectively from two phase shifting sets. This method uses defocused 1-bit binary patterns to bypass rigid camera-projector synchronization, which has potential for high-speed applications.
KEYWORDS: 3D image reconstruction, High dynamic range imaging, 3D metrology, Cameras, 3D image processing, Image quality, 3D acquisition, Fringe analysis
The paper proposes a new method for measuring the 3D shape of fast-moving highly reflective surfaces by using the transitioning state of the digital micro-mirror device (DMD). 1-bit binary patterns are used to achieve kHz measurement speeds and to overcome the rigid camera-projection synchronization requirement. More than one captures of the fringes are made during each cycle of the pattern projection. The dark period between DMD’s ON time is used to alleviate saturation problem of highly reflective surfaces. Experiments conducted demonstrate the success of the proposed method for measuring fast-moving shiny surfaces with an image acquisition speed of 1,000 Hz
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