Structured Light Three-dimensional Measurement Research Articles

Three-dimensional measurement based on equal spacing binary fringe coding

Abstract Binary fringe projection technology can effectively avoid the measurement error caused by nonlinearity in structured light three-dimensional measurement system. In this paper, a binary fringe projection coding based on equal spacing is proposed Firstly, the image sequence projected by binary fringes with equal spacing is corresponding to the sinusoidal intensity values in the same period one by one, and then the sinusoidal fringes are generated by weighted superposition. The experimental results show that, compared with the traditional four-step and 12-step phase shifting methods, the mean square error of the synthesized sinusoidal pattern is reduced by 36.74% and 18.24% respectively, and the mean square error of the distance between the obtained spherical point cloud of the standard sphere and the center of the fitting standard sphere is reduced by 89.36% and 77.27% respectively.

A Novel Generalized Adaptive Domain Fusion Framework for Structured Light 3-D Measurement

A Novel Generalized Adaptive Domain Fusion Framework for Structured Light 3-D Measurement

Efficient and accurate projector calibration method based on phase-shifting method with sinusoidal structured light

ObjectiveProjector calibration is one of the most basic and important steps in structured light three-dimensional measurement. However, such as complicated calibration process and low accuracy are still the inevitable problems in the calibration process. In this paper, a projector calibration method based on phase-shifting method with sinusoidal structured light is proposed to improve the accuracy of the calibration and simplify the operation of the calibration. MethodsFirstly, projecting a set of sinusoidal fringes onto a black-and-white circular calibration board, and collecting the images synchronously by a CCD camera; Secondly, establishing the correspondence between camera pixels and projector pixels by using the consistency of phase information which means that the absolute phase value of an arbitrary point on the calibration board is equal to the absolute phase value of this point in the camera image and virtual projector image; And then a set of virtual DMD images on the projector can be obtained by using the principle above; Finally, using this set of virtual DMD images, the parameters of the projector can be calibrated with camera calibration method based on circular calibration board. ResultsThe experimental results show that the maximum reprojection error of the projector calibrated by this method is 0.0419 pixels, and the average reprojection error is 0.0343 pixels. The equipment involved in the calibration process is simple and the experimental operation is easy. The experimental results indicated that this method has high calibration accuracy and efficiency.

Phase unwrapping technology for structured light three-dimensional measurement: A review (invited)

Phase unwrapping technology for structured light three-dimensional measurement: A review (invited)

Dual-Frequency Phase Unwrapping Method for anti-Jump Errors of Wrapped Phase

The accuracy of stripe structured light three-dimensional measurement is greatly improved with the development of hardware and image processing technology. However, the fault tolerance and anti-jamming ability of complex measured objects need to be improved. First, by aiming at the problem of large error caused via wavelength position jump in phase unwrapping, the shortcomings of single-frequency phase unwrapping method were analyzed, a dual-frequency phase unwrapping method was proposed, and its mathematical model was established. Second, the error tolerance was analyzed near the dual-frequency phase hopping point, and the maximum error tolerance value is 0.25δ. In the environment of interference and noninterference, the three-dimensional measurement experiment shows that the mathematical model of dual-frequency phase unwrapping and the theoretical correctness of error analysis. Its measurement accuracy and anti-interference ability are higher than those of single-frequency phase unwrapping. Also, it can suppress the gross error caused by wavelength dislocation effectively, and the operation is simple. Aiming at three-dimensional measurement and reconstruction of highly complex surface with self-occlusion, the local reconstructed has high accuracy, and the reconstructed surface is smooth. It corresponds to the real measured surface and has good anti-interference performance.

U-Net-based Structured Light Three-dimensional Measurement Technology

U-Net-based Structured Light Three-dimensional Measurement Technology

Development and application of a non-destructive pavement testing system based on linear structured light three-dimensional measurement

Automatic detection dramatically improves the efficiency and accuracy of asphalt pavement inspection. However, the existing detection systems cannot coordinate the balance between efficiency and accuracy. Three-dimensional pavement detection was proposed and developed in this article. The theoretical model of camera imaging was first established based on optical triangulation. The camera’s intrinsic and extrinsic parameters were evaluated by utilizing a checkerboard calibration target, and the camera lens distortion was also considered to ensure the accuracy of the three-dimensional measurements. The subpixel coordinates of the single-stripe center were extracted based on two-dimensional image processing technology, and then the pixel coordinates were converted into real-world elevation coordinates based on the camera imaging model. The cubic spline method and the three-dimensional data filtering method based on the pavement surface profile were applied to restore the data and remove the noise, respectively. Then the three-dimensional reconstruction was achieved based on Delaunay triangulation algorithm. We expect that this new system can significantly reduce the costs without decreasing the test accuracy, thus making large-scale engineering applications viable.

Camera–projector system calibration method based on optimal polarization angle

In the structured light three-dimensional measurement system, calibration is crucial for measurement accuracy. However, conventional projector calibration methods involve complicated procedures. Therefore, a novel method is developed for projector calibration. The key concept is to establish the relationship between projector coordinates and the world coordinates using the projection checkerboard, which enables the calibration of the projector to be the same as that of a camera. In addition, the edges of the checkerboard form different degrees of high-light regions when the projection checkerboard is collected. These high-light regions affect the extraction of corner points and cause low accuracy of the projector calibration. Therefore, the projection checkerboard is collected by a CCD camera equipped with a polarizer at the optimal polarization angle. Then the subpixel corner extraction algorithm based on the homography matrix mapping is used to extract the subpixel coordinates of the corners. Finally, the projector can be calibrated with the same method as the camera. In the experimental part, the validity of the method is verified by the reprojection system.

Light plane calibration and accuracy analysis for multi-line structured light vision measurement system

This paper investigates the overall fitting accuracy of the light plane can be improved by changing the relative distance between camera and laser, altering the projection direction of the light stripe and increasing the number of extracted light stripe in the multi-line structure light measurement system. Firstly, a multi-line structured light three-dimensional measurement system platform is built, and the existing calibration plate is modified according to the requirements of the experimental design. Then, laser stripes are projected onto a blank area in the checkerboard to facilitate the extraction of the centerline of the light stripe. Moreover, the three-dimensional (3D) point cloud transformed from centerline of each stripe is used to fit into a plane by a random sample consensus algorithm (RANSAC). Finally, the influence of different experiment methods on the overall fitting accuracy of the light plane is observed. Experiments illustrate that the proposed experimental methods can reduce the relative error of the overall fitting result of the multi-line structured light plane by more than two times, and the overall calibration accuracy of the light plane is improved in terms of the error of angle between the calibrated light planes.

Improving the extracting precision of stripe center for structured light measurement

The accuracy of the stripe center extraction is affected by the uneven reflectance and large curvature change of the object surface in the structured light three-dimensional measurement system. Aiming to eliminate the stripe distortion and improve the accuracy of stripe center extraction, an improved stripe center extraction method is proposed for structured light measurement. By analyzing the principle of stripe distortion and the types of stripe noises, the mean filtering is used to eliminate the noises. Then, a stripe preprocessing method is presented to adjust the gray scale of stripe distortion. Finally, stripe centers are extracted through the curve fitting method by preprocessing. Furthermore, the proposed method addressed the problem of local discontinuity of the stripe center caused by the unevenness of brightness in the measurement of complex surface profiles. The proposed method has been validated and verified by experiments. A high accuracy in the extraction of strip centers could be obtained.

Structured Light Three-Dimensional Measurement Based on Machine Learning.

The three-dimensional measurement of structured light is commonly used and has widespread applications in many industries. In this study, machine learning is used for structured light 3D measurement to recover the phase distribution of the measured object by employing two machine learning models. Without phase shift, the measurement operational complexity and computation time decline renders real-time measurement possible. Finally, a grating-based structured light measurement system is constructed, and machine learning is used to recover the phase. The calculated phase of distribution is wrapped in only one dimension and not in two dimensions, as in other methods. The measurement error is observed to be under 1%.

Out-of-Focus Projector Calibration Method with Distortion Correction on the Projection Plane in the Structured Light Three-Dimensional Measurement System

The three-dimensional measurement system with a binary defocusing technique is widely applied in diverse fields. The measurement accuracy is mainly determined by out-of-focus projector calibration accuracy. In this paper, a high-precision out-of-focus projector calibration method that is based on distortion correction on the projection plane and nonlinear optimization algorithm is proposed. To this end, the paper experimentally presents the principle that the projector has noticeable distortions outside its focus plane. In terms of this principle, the proposed method uses a high-order radial and tangential lens distortion representation on the projection plane to correct the calibration residuals caused by projection distortion. The final accuracy parameters of out-of-focus projector were obtained using a nonlinear optimization algorithm with good initial values, which were provided by coarsely calibrating the parameters of the out-of-focus projector on the focal and projection planes. Finally, the experimental results demonstrated that the proposed method can accuracy calibrate an out-of-focus projector, regardless of the amount of defocusing.

Three-line structured light measurement system and its application in ball diameter measurement

This paper proposes a three-dimensional measurement system of three-line structured light for ball diameter. In the system, firstly, the BP neural network is used to correct the distortion model of the camera. Zhang Zhenyou’s plane calibration method is adopted to get the camera's intrinsic and extrinsic parameters. Secondly, a sub-pixel extraction method for the center of the three-line structured light stripe is put forward to achieve sub-pixel accuracy, which is integrated by the adaptive median filtering method, threshold segmentation method, mean square gray gradient method and weighted gray center of gravity method. Finally, a three-line structured light three-dimensional measurement platform is developed, and the ball diameter measurement is carried out. It shows that the proposed method is valid, flexible and with high precision by experiment, and the three-line structured light three-dimensional measurement system can meet the requirements of high-precision and speed.

A Study on the Approach of the Structured Light Three-dimensional Measurement

A Study on the Approach of the Structured Light Three-dimensional Measurement

Research of Image Information Extraction Method Based on Structured Light

In line structured light three-dimensional measurement systems, the position of shifted light in the structure light image reflects the three-dimensional profile information of the object. In this paper, according to the characteristics of structured light image, a approach of separating shifted pixels is proposed, and successfully extracts structured light image two-dimensional data with related mathematical methods, which contributes to the foundation for structured light three-dimensional reconstruction of three-dimensional measurement system work.

面向结构光三维测量的高稳定映射拼接方法

面向结构光三维测量的高稳定映射拼接方法

Projector calibration with error surface compensation method in the structured light three-dimensional measurement system

In the structured light three-dimensional measurement system, calibration is the key to the measurement accuracy; however, conventional calibration methods for the projector are either too complex or inaccurate. Therefore, we propose a simple and accurate method to calibrate the projector. In this method, the calibration points in the camera image plane can be mapped to the projector according the homography of the planar projection. In addition, an error surface compensation method is developed to minimize mapping errors caused by lens distortion of the camera and projector. As a result, the projector can be calibrated with the same method as the camera. Experiments are conducted to verify the effectiveness of the proposed method.

Practical Technologies Research of Line Structured Light Three-Dimensional Profile Measurement at Low-Cost

In this paper, a new method for determining the integrity of the image element of the target was proposed based on the self-made low-cost line structured light three-dimensional measurement platform, and BP neural network was used to complete the calibration of line structured light camera system. At the same time, Gaussian model for the four direction were constructed , which speeds up the extraction speed for the laser stripe center based on the gray gravity method of skeleton, and the point cloud data is deal with the refinement, noise removing, smoothing and three-dimensional reconstruction, which complete the task of product three-dimensional contour detection.