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Digital fringe projection is one of the most widely adopted optical non-contact methods used for high-precision depth measurement in industry. Nevertheless, new approaches with less measurement complexity and higher accuracy are still emerging in the research field. In this paper, we first analyze the efficiency of the reference-plane-based dual-fr...
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We present a novel deep learning-based quantification pipeline for the analysis of cell culture images acquired by lens-free microscopy. The image reconstruction part of the pipeline features a convolutional neural network performing phase unwrapping and accelerating the inverse problem optimization. It allows phase retrieval at the 4K level (3,840...
![The principle of Zhang’s method [36]. (a) The three-step phase-shifting...](publication/330647111/figure/fig1/AS:11431281253123629@1718826771526/The-principle-of-Zhangs-method-36-a-The-three-step-phase-shifting-patterns-b-The_Q320.jpg)
In this paper, we propose a high-speed 3D shape measurement technique based on the optimized composite fringe patterns and stereo-assisted structured light system. Stereo phase unwrapping, as a new-fashioned method for absolute phase retrieval based on the multi-view geometric constraints, can eliminate the phase ambiguities and obtain a continuous...
Abstract Background In the fast 3D shape measurement, it is an important factor to use the least number of fringe patterns to get the wrapped phase and the wrapped phase is always required to be retrieved to absolute phase. But the process of phase unwrapping may affect the quality of absolute phase. Besides absolute phase retrieval is time-costing...
Fringe projection profilometry (FPP) is one of the most popular three-dimensional (3D) shape measurement techniques, and has becoming more prevalently adopted in intelligent manufacturing, defect detection and some other important applications. In FPP, how to efficiently recover the absolute phase has always been a great challenge. The stereo phase...
Reducing the number of images in fringe projection profilometry has emerged as a significant research focus. Traditional temporal phase unwrapping algorithms typically require an additional set of coding fringe or phase shift fringe images to determine the fringe order and facilitate phase unwrapping, in addition to the essential sinusoidal phase s...
Citations
... For traditional PSP, the main phase unwrapping methods have spatial phase unwrapping [25,26] and temporal phase unwrapping (TPU) [27,28]. For ordinary objects, surface discontinuities are common rules rather than exceptions. ...
Phase shifting algorithm, which is well-known for its high-accuracy and high-resolution, plays a crucial role in fringe projection profilometry. A class of variant shifting-phase coding method (VSPCM) has been proposed for high-speed 3D measurement. The three kinds of VSPCM include the inner shifting-phase method (ISPM), the intensity-coded method (ICM) and the modified Carré algorithm (MCA). These methods project only four patterns avoiding the need for extra images, yet achieve accuracy comparable to the classical three-frequency heterodyne method. In VSPCM, the shifting-phase, as a key code-word for phase unwrapping, is encoded as a variable value. In practice, the noise and the encoding of shifting-phase have varying degrees of impact on the performance of these methods. But the coded ranges of the shifting-phase were previouly empirical values. Besides, there are no studies related to these factors, and also a lack of comparative researches on such methods. This paper compares three kinds of VSPCM for the first time. We derive the noise error models for shifting-phase and wrapped phase in three methods and examine the impact of variant shifting-phase on fringe orders and wrapped phase in these methods. We find that the abnormal shifting-phase errors predominantly cause fringe orders errors. Fortunately, median filtering can effectively handle shifting-phase errors to ensure successful phase unwrapping. To improve their accuracy, we also deduce that the optimal shifting-phase encoding range is [−77°, 77°] for ISPM, and is [−61°, 61°] for ICM, and is [34°, 74°] for MCA. For wrapped phase errors, the distributions of ICM and MCA exhibit a U-shaped distribution, while ISPM demonstrates a uniform distribution. Based on theoretical analysis and experiment results, this paper gives recommendations for better use of these methods to boost their accuracy and offers valuable guidance for selecting an appropriate VSPCM under the specific measurement requirements.
... The recovery of the absolute phase is limited by the depth of the scene. Yidan Xing and Chenggen Quan [50] proposed a new phase unwrapping method (ERDF) for an accurate calculation of the absolute phase. This method only needs to calculate the phase based on two sets of fringe patterns. ...
The three-dimensional (3D) size and morphology of high-temperature metal components need to be measured in real time during manufacturing processes, such as forging and rolling. Since the surface temperature of a metal component is very high during the forming and manufacturing process, manually measuring the size of a metal component at a close distance is difficult; hence, a non-contact measurement technology is required to complete the measurement. Recently, machine vision technology has been developed, which is a non-contact measurement technology that only needs to capture multiple images of a measured object to obtain the 3D size and morphology information, and this technology can be used in some extreme conditions. Machine vision technology has been widely used in industrial, agricultural, military and other fields, especially fields involving various high-temperature metal components. This paper provides a comprehensive review of the application of machine vision technology in measuring the 3D size and morphology of high-temperature metal components. Furthermore, according to the principle and method of measuring equipment structures, this review highlights two aspects in detail: laser scanning measurement and multi-view stereo vision technology. Special attention is paid to each method through comparisons and analyses to provide essential technical references for subsequent researchers.
... However, the measurement speed is limited because of the complex correlation algorithm. Dual frequency absolute phase retrieval methods are also widely used in fast 3D measurements [27,[32][33][34][35][36]. The commonly used phase unwrapping technique projects a coarse unit frequency image and uses the calculated phase to help unwrap the more accurate phase maps [27,37]. ...
... However, the frequency still cannot be too high because the noise will cause phase order deviations. Dual frequency methods based on reference plane [32] and geometric constraints [38] have been proposed to retrieve the absolute phase from fringe images with a higher frequency. The phase of the fringe with a relatively lower frequency is unwrapped first based on some spatial information. ...
In three-dimensional (3D) shape measurement applications based on absolute phase matching in fringe projection profilometry, measurement accuracy can be improved by using denser fringes under the pre-condition that the phase ambiguities can be successfully removed after phase unwrapping. In real-time measurement situations, the number of fringe patterns is limited to reduce motion-induced errors, which does, however, pose more difficulties for the absolute phase recovery of dense fringes. In this paper, we propose a stereo phase matching method that takes advantage of the high accuracy of denser fringes and the high efficiency of using only two different fringe frequencies. The phase map is divided into several sub-areas, and in each sub-area the phase is unwrapped independently. The stereo-matched pixel is selected from the distributed candidates in these sub-areas by geometric constraints. Experimental results show that only five patterns are needed to perform a high-accuracy real-time 3D measurement of the thermally induced deformation of the sample under different heating temperatures based on a telecentric stereo microscopic system.
As one of the most popular techniques for non-contact three-dimensional (3D) sensing/imaging, fringe projection profilometry (FPP) has been growing rapidly over the past decades partially because of the improved speed of computing devices and reduced cost of hardware. 3D optical sensing has started being an integral part of our daily lives such as Face ID enabled by 3D sensors on smart phones. The impact of such techniques can be even greater with the ever-growing artificial intelligent (AI), machine learning, smart manufacturing, robotics as well as other fields. However, there are still fundamental challenges to be tackled to make such advanced optical sensing techniques ubiquitous. This paper presents the current status of FPP techniques, the major challenges still facing in the field, and our perspectives on the future of FPP techniques.
