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- 摘要
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- 实验方案
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Research on multi-camera calibration and point cloud correction method based on three-dimensional calibration object
摘要： The single camera measurement system can’t obtain all the surface information of the object limited by the field of view, thus it can’t achieve complete measurement of the object. Multi-camera system can overcome this difficulty. But it is difficult to unify the coordinate system of distinct cameras. In order to solve this problem, a global calibration method of multi-camera system is proposed. A three-dimensional cube calibration object is designed. Every camera is only calibrated on one surface of the cube calibration object. Because different surfaces of the cube calibration object are in a unified world coordinate, the coordinates of the feature points on different surfaces are naturally in the unified world coordinate system. Thus global calibration can be completed by calibrating multiple cameras at the same time. In addition, to minimize the error of calibration, a correction method is proposed. The correction parameters are obtained by the deviation between the world coordinates and the reconstructed coordinates of the feature points on calibration object. The parameters are applied to the measurement to improve the accuracy of the whole point cloud. Experiments are carried out on a multi-camera measurement system, and the results show that the method proposed in this paper is effective and feasible.
关键词： Calibration,Measurement,3D calibration object,Fringe projection,Multi-camera
更新于2025-09-23 15:23:52
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Inverse projected-fringe technique for measurement of dimensions and surface profile of axisymmetric objects
摘要： An inverse projected-fringe technique based on simulating the system of a projector-part-camera is proposed for an on-machine inspection of axisymmetric parts. Parts considered for this study are relatively large, have high specular surfaces and have sharp slopes. A computer simulation-based method and the CAD model of the part was used to produce the inverse fringes as well as to find an appropriate trace passing through the symmetrical axis of the part that offers the best signal to noise ratio. This technique measures the deviation from a master-part and provides an accuracy of better than 10 microns for the part with a radial dimension of about 10 cm. It is shown that the proposed technique improves the signal to noise ratio and the repeatability of the system compared to the standard fringe projection technique, in particular for the areas with a steep slope.
关键词： Fringe projection,Structured light,Inverse fringe projection,Optical metrology,Quality control
更新于2025-09-23 15:21:01
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Deep-learning-enabled geometric constraints and phase unwrapping for single-shot absolute 3D shape measurement
摘要： Fringe projection profilometry (FPP) has become a more prevalently adopted technique in intelligent manufacturing, defect detection, and some other important applications. In FPP, efficiently recovering the absolute phase has always been a great challenge. The stereo phase unwrapping (SPU) technologies based on geometric constraints can eliminate phase ambiguity without projecting any additional patterns, which maximizes the efficiency of the retrieval of the absolute phase. Inspired by recent successes of deep learning for phase analysis, we demonstrate that deep learning can be an effective tool that organically unifies phase retrieval, geometric constraints, and phase unwrapping into a comprehensive framework. Driven by extensive training datasets, the neural network can gradually “learn” to transfer one high-frequency fringe pattern into the “physically meaningful” and “most likely” absolute phase, instead of “step by step” as in conventional approaches. Based on the properly trained framework, high-quality phase retrieval and robust phase ambiguity removal can be achieved only on a single-frame projection. Experimental results demonstrate that compared with traditional SPU, our method can more efficiently and stably unwrap the phase of dense fringe images in a larger measurement volume with fewer camera views. Limitations about the proposed approach are also discussed. We believe that the proposed approach represents an important step forward in high-speed, high-accuracy, motion-artifacts-free absolute 3D shape measurement for complicated objects from a single fringe pattern.
关键词： Deep learning,Phase unwrapping,Fringe projection profilometry,Geometric constraints,Single-shot absolute 3D shape measurement
更新于2025-09-23 15:21:01
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Online dimensional control of rolled steel profiles using projected fringes
摘要： Fringe projection is a versatile method for mapping the topography of surfaces. In this paper, it is used to measure the defects on the head of railroad rails while the rails are moving. Railroad rails are made by hot rolling. The quality of the finished product is generally good, but surface texture will deteriorate with increasing temperature. A method for online inspection therefore is very desirable. In the present experiment, dimensional inspection of the railroad rails was made online while moving at a speed of 1–2 m/s. Therefore, it is important to minimize the registration time. To achieve this, we apply a method of fringe location with sub-pixel accuracy that requires only a single exposure for each registration.
关键词： Fringe projection,Railroad rails,Optical measurements
更新于2025-09-23 15:21:01
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Directly recognizing and removing the projector nonlinearity errors from a phase map in phase-shifting fringe projection profilometry
摘要： In phase-shifting fringe projection profilometry, the projector nonlinearity has been recognized as one of the main error-inducing factors, especially when only very few fringe patterns are available. For solving this issue, this paper presents a simple and effective method, that allows us to recognize and remove, directly from a calculated phase map, the nonlinearity-induced errors without calibrating the projector luminance or the phase errors in advance. In implementation, after filtering the phase map using a low-pass filter, we estimate the phase error coefficients by exploiting the dependence between the isolated artifacts and the smoothed phases under 3-sigma criterion. Furthermore, using the phase error function just estimated, the phase errors are corrected in a pointwise way through fixed-point iterations. Experimental results demonstrated that this method offers some advantages over others, such as being independent of a special nonlinearity model, being easy to implement and not requiring a prior calibration, protecting the edges and details of the measured shape from being blurred, and enabling dealing with time-variant projector nonlinearities.
关键词： Fringe projection profilometry,Phase shifting,Projector nonlinearity
更新于2025-09-10 09:29:36
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[IEEE 2017 14th IEEE India Council International Conference (INDICON) - Roorkee (2017.12.15-2017.12.17)] 2017 14th IEEE India Council International Conference (INDICON) - Optical Image Encryption using Fringe Projection Profilometry, Fourier Fringe Analysis, and RSA Algorithm
摘要： Optical image encryption is one of the most promising technologies being investigated in the field of data communication and information technology. In this paper, a novel image encryption system based on virtual optical technique, Fourier transform phase retrieval algorithm and RSA public key exchange is proposed. In this strategy, a gray-level image is captured using a digital camera and encrypted using a linear grating superposed on the reflected intensity map of the object. A speckle mask is simulated and used as a secret key in both transmission and reception ends so that the receiver can identify the authenticity of the ciphertext by using the speckle pattern in the decryption process. The decryption method is performed to recover the phase of the deformed grating pattern. Towards this, Fourier transform based phase retrieval and sequential line scan phase unwrapping algorithm is utilized. The simulation results demonstrate the validity of the encryption method and the high robustness against potential attacks. To determines the accuracy of the information retrieved by the proposed technique, root mean square error is calculated between the original image and retrieved image. The proposed technique is also applicable for the information authentication.
关键词： encryption,image processing,phase detection,fringe projection,security
更新于2025-09-09 09:28:46
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Person Recognition Using 3-D Palmprint Data Based on Full-Field Sinusoidal Fringe Projection
摘要： Palmprint-based biometrics has been widely studied for human recognition. However, for feature extraction and matching, most of the current systems use a 2-D image, which can be easily forged. As depth information is included, 3-D palmprints are more competitive in anticounterfeiting. This paper presents a novel person recognition method using 3-D palmprint data. The full-field sinusoidal fringe projection technique is employed to collect 3-D palmprint data remotely and quickly, from which the orientation feature of the mean curvature image is extracted through a revised Gabor filter. An effective feature matching strategy called the binary code list is proposed for classification. Using the developed capture system, a 3-D palmprint database is established, and verification and identification experiments are performed. The PolyU 3-D palmprint database is also used to evaluate the performance of the proposed recognition method. Compared with traditional single-mode feature-based 3-D palmprint recognition methods, the proposed method is more accurate, efficient, and faster.
关键词： person recognition,binary code list,3-D palmprint,Gabor filter,fringe projection,mean curvature image (MCI)
更新于2025-09-09 09:28:46
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Rapid tracking of extrinsic projector parameters in fringe projection using machine learning
摘要： In this work, we propose to enable the angular re-orientation of a projector within a fringe projection system in real-time without the need for re-calibrating the system. The estimation of the extrinsic orientation parameters of the projector is performed using a convolutional neural network and images acquired from the camera in the setup. The convolutional neural network was trained to classify the azimuth and elevation angles of the projector approximated by a point source through shadow images of the measured object. The images used to train the neural network were generated through the use of CAD rendering, by simulating the illumination of the object model from di?erent directions and then rendering an image of its shadow. The accuracy to which the azimuth and elevation angles are estimated is within 1 classi?cation bin, where 1 bin is designated as a ± 10° patch of the illumination dome. To evaluate use of the proposed system in fringe projection, a pyramidal additively manufactured object was measured. The point clouds generated using the proposed method were compared to those obtained by an established fringe projection calibration method. The maximum dimensional error in the point cloud generated when using the convolutional network as compared to the established calibration method for the object measured was found to be 1.05 mm on average.
关键词： real-time tracking,convolutional neural network,fringe projection,machine learning,projector calibration
更新于2025-09-04 15:30:14