Measurement technology based on a Stokes parametric polarization system.

Structured light measurement systems often use polarization filters to reduce image interference from highly reflective areas. This method can be effective, but it may also reduce the brightness of specific areas, particularly overly dark portions, which can affect the accuracy of the measurement results. This paper proposes a measurement method for a polarization system based on Stokes parameters to solve the problem. After adjusting the polarization filter to angles of 0°, 45°, and 90°, the camera captures an image of the object and calculates the corresponding Stokes parameters to generate the expected polarization angle histogram. Then, based on the detailed information on the angle distribution, the accurate mathematical model is used to screen the interval, and the optimal polarization angle is determined by orthogonal processing while ensuring the signal-to-noise ratio and image quality. Finally, an image fusion technology synthesizes a set of fringe projection images with the preferred polarization angles. Experiments have shown that this new method effectively addresses the issue of interference in the highlighted region when using conventional polarization filters. Additionally, it significantly improves the quality of the fringe pattern. The polarization angle selection in the experimental process is made more rapid and accurate through the quantitative mathematical model calculation of the polarization angle, significantly improving the system's measurement efficiency.

Three-dimensional reconstruction of polarized ambient light separation in complex illumination.

In current research, it is still a hot topic for 3D reconstruction under complex illumination. This paper uses a polarization camera combined with a coding technique to propose a new 3D reconstruction method for polarized ambient light separation. Based on the polarization camera, a specific separation model is established to analyze the relationship between the polarization characteristics of polarized and natural light. Specular reflections were filtered first and then analyzed based on the stocks vector and muller matrix. A specific calculation process was used to calculate different polarization azimuths according to the polarization characteristics, and finally, the polarized light and ambient light were separated. The experimental results show that the use of this polarization camera approach reduces the number of steps required to rotate the polarizer multiple times. This not only reduces the shooting time but also improves the efficiency. Moreover, after separating the ambient light, polarization imaging suppresses the interference of the ambient light, which helps to highlight the complete point cloud image more clearly in the 3D reconstruction. The standard deviation of 3D reconstruction was improved to 0.1675 mm by using this method in indoor and outdoor experiments.

Robust structured light 3D measurement method based on polarization-encoded projection patterns.

Fringe projection profilometry (FPP) is widely used in 3D vision measurement because of its high robustness and measurement accuracy. In the case of HDR objects, due to the problem of surface reflectivity, the obtained image will be overexposed. This will cause the sinusoidality of the fringes projected on the surface of the object in the acquired image to be interfered, resulting in a phase error in the calculated wrapped phase. Therefore, a polarization-encoded sinusoidal structured light is proposed to enhance the sinusoidality of the fringe. The phase information contained in the polarized sinusoidal structured light fringe is only related to the polarization state, not to the light intensity. A polarization coding assisted structured light measurement strategy (PASM) is proposed. This method uses polarization coding assisted polarization phase-shifting fringes for phase unwrapping. The angle of the linear polarizer is set to zero in this method, and it does not require rotating the polarizer. It only needs a single exposure to improve the fringe quality and obtain a more stable unwrapping phase. The experimental results show that the obtained polarization fringes have better sinusoidality, and the phase unwrapping can be more accurate. The reconstructed 3D point cloud also does not appear missing and has better accuracy. It is a reliable method for vision measurement of HDR objects.

3D reconstruction method based on the multi-polarization superposition coding phase pattern of LRR objects.

Conventional research in structured light measurements has utilized light intensity as a channel for information. The polarization of light can be used as an additional channel of information. In this paper, a method based on the superposition of multiple polarization states is proposed to encode structured light. By building a polarization model between the color of light and the polarization states, polarized structured light containing phase information is obtained without rotating the polarizer. It is demonstrated that the method improves the waveform quality of stripes and the accuracy of the 3D reconstruction results when measuring highly reflective objects.

Calibration method of line-structured light sensors based on a hinge-connected target with arbitrary pinch angles.

Line-structured light 3D measurement is often used for 3D contour reconstruction of objects in complex industrial environments, where light plane calibration is a key step. In this paper, we propose a calibration method for a line-structured optical system based on a hinge-connected double-checkerboards stereo target. First, the target is moved randomly in multiple positions at any angle within the camera measurement space. Then, by acquiring any one image of the target with line-structured light, the 3D coordinates of the light stripes feature points are solved with the help of the external parameter matrix of the target plane and the camera coordinate system. Finally, the coordinate point cloud is denoised and used to quadratically fit the light plane. Compared with the traditional line-structured measurement system, the proposed method can acquire two calibration images at once; thus, only one image of line-structured light is needed to complete the light plane calibration. There is no strict requirement for the target pinch angle and placement, which improve system calibration speed with high accuracy. The experimental results show that the maximum RMS error of this method is 0.075 mm, and the operation is simpler and more effective to meet the technical requirements of industrial 3D measurement.

Specular flare suppression method for reflective materials based on the optimal polarizing angle.

A specular suppression model on reflective material figures based on polarization information and figure grayscale information is built. The model can optimize the imaging effect of reflective material in a strong light environment to restore the information characteristics of the figure. Taking the workpiece surface of reflective material as the experimental object, figure surfaced information restoration and visual measurement effect analysis were carried out. The experimental results show that the method offered can achieve good suppression of the large-area light spot phenomenon in the imaging of reflective material. The texture contours of the figures are significantly improved, and the imaging indicators in all aspects are further optimized, which verifies the feasibility of the offered method to a certain extent.

Global calibration method for non-overlapping cameras based on rigidly connected stereo targets.

In complex field of view (FOV) environments, a single camera's FOV measurement range is limited and cannot cover the entire object under test for global calibration. Multiple cameras are used mostly for large FOV environment measurements, but the traditional one- and two-dimensional targets used for global calibration in large FOV environments are prone to overlapping FOV. Furthermore, other large-sized targets are difficult to produce and process, and the laser projection method and plane mirror calibration methods are easily affected by the outdoor environment. To solve this problem, a non-common FOV binocular calibration method based on rigidly connected stereo targets is proposed. The calibration process is as follows: First, the rigidly connected target, which is composed of two plane targets with a checkerboard, is placed in front of the two cameras, and the vision sensor captures the corresponding sub-target image; then, the target is moved multiple times, and the transformation relationship between multiple vision sensors is obtained according to the spatial constraint characteristics of the rigidly connected target. Hence, the method overcomes the limitation of the non-overlapping FOV calibration method that relies on large measuring instruments. The experimental results show that the RMS error of the 13 mm distance is 0.16 mm. The proposed method is effective, simpler to operate than other methods, and does not rely on the constraint of complex targets. More importantly, this measurement method solves the difficult problem of measurement in non-public FOV, meeting the requirements of large FOV measurement ranges.

3D reconstruction method based on the optimal projection intensity of a polarization system.

The measurement of shiny objects is a major challenge for structured light 3D measurement. Polarization systems can be used to measure shiny objects. However, the polarizer may attenuate the light intensity of the captured image, reducing the SNR of the image, and the measurement accuracy will be affected. To improve the measurement accuracy and efficiency, this paper proposes a 3D measurement method based on polarization optimal projection intensity. By establishing the camera response function under the polarization system, the desired optimal projection intensity can be directly estimated and used to compensate for the image light intensity attenuated by the additional polarizer. This method does not require rotating polarizers and multiple exposure times. In addition, the optimal fringe images are obtained by applying image fusion algorithms. The experimental results show that the method improves pixels in the image that are too dark, while significantly reducing the saturated pixels on the shiny surface. This method can effectively improve the image contrast, get better fringe images, extract more effective information, and reconstruct a more complete 3D point cloud.

Rapid 3D reconstruction method based on the polarization-enhanced fringe pattern of an HDR object.

Measurement of high dynamic range objects is an obstacle in structured light 3D measurement. They entail both over-exposed and low-exposed pixels in a single exposure. This paper proposed a polarization-enhanced fringe pattern (PEFP) method that a high dynamic range image can be obtained within a single exposure time. The degree of linear polarization (DOLP) is calculated using the polarization properties of reflected light and a linear polarizer in fixed azimuth in this method. The DOLP is efficiently estimated by the projected polarization-state-encode (PSE) pattern, and it does not need to change the state of the polarizer. The DOLP depends on light intensity rather than the reflectivity of the object surfaces indicated in experimental results. The contrast of fringe patterns was enhanced, and the quality of fringe patterns was improved by the proposed method. More sufficient 3D point clouds and high-quality shape can be recovered using this method.

Use of color information for structured-light 3D shape measurement of objects with shiny surfaces.

Objects with shiny surfaces cannot be directly measured using the conventional structured-light method. To cope with this problem, in this paper, we propose a novel method for removing the saturated components in an image. First, the specular pixels in the image are identified using a highlight extraction algorithm. Then, based on the reflection component separation (RCS) theory, the diffuse and specular components of these specular pixels are separated. For objects with shiny surfaces, use of the RCS approach destroys the color information of highlighted pixels with a large specular reflection component. As such, finally, the color information of the highlighted pixels is recovered using an image repair process. Experimental results indicate that 95% of the highlights in the images were eliminated. The highlight caused by the strong reflecting surface can be well suppressed. This proposed method effectively overcomes the interference of reflected light and provides a feasible solution to the problems associated with the structured-light measurement of objects with smooth surfaces.

Design of a free-form surface microlens array optical system with high efficiency and uniformity.

The microlens array has been widely applied in LED lighting source due to its special optical properties, but most of the research lacks the analysis and optimization of the complete mathematical models. Hence, the new design method of a free-form surface microlens array optical system is proposed in this paper. Based on the characteristics of TIR and the law of refraction, a complete mathematical model of the free-form microlens is established. By numerically solving a set of differential equations, the profile of the free-form surface microlens is obtained. Then we rotate the profile to get the free-form surface microlens. Finally, the proposed microlens array is simulated and analyzed in near-field and far-field situations, respectively. We also discuss the influence of microlens array characteristics on illumination performance. The result shows the uniformity and efficiency have been improved, both of which can reach more than 90%.

Calibration method for a line-structured light vision sensor based on a single cylindrical target.

This paper presents a new, to the best of our knowledge, calibration method for line-structured light vision sensors. The laser stripe intersecting the cylindrical target and the line-structured light is captured by the camera, and the light plane parameters of the line-structured light are obtained by combining the cross-sectional characteristics of the ellipse. The nonlinear optimization of the light plane parameters use multiple locations to get the optimal solution of the light plane equation. This method requires only a single cylindrical target, which in turn greatly simplifies the calibration process. The results of simulation experiments and physical experiments show that the proposed calibration method can achieve higher calibration accuracy and measurement accuracy. The effectiveness of the new calibration method is verified.

Polarized-state-based coding strategy and phase image estimation method for robust 3D measurement.

Polarized structured light is a novel method to measure shiny surface. However, the SNR of the captured image was affected by the additional polarizing filter. And the blurred influence of camera defocus was also strengthened. The accuracy of fringe edges detection was reduced. In this paper, a polarized-state-based structured light coding strategy and a phase image estimation method are proposed to improve the measurement robustness. To preserve the coding message in the complex environment, a special polarized-state-based coding strategy is adopted. To reduce the error which induced by additional polarizing filter and extracting the information from the saturated areas as much as possible, a phase image estimation method based on Stokes parameter is proposed. Compared with the traditional polarization-based structured light system, the experimental setup of proposed method is configured without any additional hardware. The experiment shows that the interference of camera defocus is remarkably reduced and the robustness of fringe edges detection is improved.

Evaluation of the relationship between T663A polymorphism in the alpha-epithelial sodium channel gene and essential hypertension.

OBJECTIVES: To evaluate the relationship between alpha epithelial sodium channel (alpha-ENaC) T663A polymorphism and the risk of essential hypertension.  METHODS: This meta-analysis was conducted between November 2014 and February 2015 in Shanghai Medical Instrumentation College, Shanghai, China. We collected all published available case-control data (N=12) identified through PubMed, Web of Science, Scopus, and Chinese National Knowledge Infrastructure (CNKI) up to December 2014. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using the fixed- or random-effect model.  RESULTS:   Although subgroup analysis showed that alpha-ENaC T663A polymorphism was associated with essential hypertension in North American individuals (OR=1.55, 95% CI=1.22-1.98, p=0.0003), our meta-analysis results did not confirm such association overall (OR=1.03, 95% CI=0.92-1.15, p=0.62). The lack of association was further confirmed by the non-superiority test (p less than 0.0001).  CONCLUSION: Alpha-ENaC T663A polymorphism might not be a risk factor for essential hypertension.

Evaluation of association of maternal IL-10 polymorphisms with risk of preeclampsia by A meta-analysis.

Emerging evidence shows that interleukin (IL)-10 gene polymorphisms can regulate its expression level and thus influence person's susceptibility to preeclampsia. However, various published results were inconsistent. To explore the association between maternal IL-10 gene polymorphisms and preeclampsia, we performed a meta-analysis based upon 11 individual studies here. Our meta-analysis results indicated that IL-10 -819 C/T (C versus T, OR = 1.28, 95% CI = 1.08-1.50, P = 0.003) and -592 C/A (C versus A, OR = 1.28, 95% CI = 1.03-1.59, P = 0.03) polymorphisms were associated with preeclampsia. Although there was no overall association between -1082 A/G polymorphism and preeclampsia (G versus A, OR = 0.93, 95% CI = 0.77-1.13, P = 0.49), such association existed among Asian (G versus A, OR = 1.29, 95% CI = 1.04-1.60, P = 0.02) and South American (G versus A, OR = 0.72, 95% CI = 0.54-0.94, P = 0.02) populations in the subgroup analysis stratified by continents.

[Hadamard transform spectral imager of adaptive spectral resolution based on DMD].

Digital micro-mirror device (DMD) can be controlled to form Hadamard encoding masks flexibly and efficiently. A kind of Hadamard transform spectral imager of adaptive spectral resolution based on DMD is proposed. The structure and the working principle of the instrument are described and the implementation method of adaptive spectral resolution is analyzed. It can adjust the spectral resolution according to the target and the observational requirements, and a reasonable compromise can be reached between the spectral accuracy and the computation of data. It not only meets the requirements of the target classification and recognition, but also improves the speed of data transmission and processing.

[Wavelength intervals selection of LED illumination for color vision application].

In color vision application, for the images with multiple colors, object can not be clearly separated from complicated background. The discrimination of the surfaces can be enhanced by selecting appropriate wavelength intervals of illumination. Firstly, the reflectance functions of all the surfaces were calibrated by four standard references. Then partial least squares method was used for selecting the effective wavelength interval of illumination. The variables important in projection (VIP) scores of wavelength intervals were considered as selection criteria. Wavelength intervals with the VIP > 1.0 were selected for illumination. Finally, three effective wavelength intervals of LED illumination were selected to separate all the surfaces of experiment image simultaneously. For separating all the surfaces of experiment image simultaneously and improving discrimination, the experiment was carried out. The experiment results demonstrate the usefulness of this method.

Comparative serum proteome analysis of human lymph node negative/positive invasive ductal carcinoma of the breast and benign breast disease controls via label-free semiquantitative shotgun technology.

Serum proteomics provides a useful tool to identify potential biomarkers associated with cancer progression. In the present study, a two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) on a linear ion trap was utilized to identify and compare serum proteins from breast cancer patients. Three groups of 21 human sera, 7 from patients with lymph node-negative invasive ductal carcinoma (IDCB), 7 from patients with lymph node-positive IDCB, and 7 controls from patients with benign breast diseases, were analyzed. Through proteomic analysis, a total of 2,078 proteins were identified with at least two unique peptide hits. By quantification with label-free spectral counting, a fruitful list of serum proteins with significant differences in abundance accompanying the progression of breast cancer was found. Through hierarchical cluster analysis based on the differently expressed proteins in selection, we found that different groups of sera could be distinguished. Among the selected proteins, tenascin-XB (TNXB) was further validated by the ELISA method in 131 serum samples as a promising biomarker for early metastasis of breast cancer. These experiments revealed the valuable potential of label-free quantitative 2D-LC-MS/MS for identification of novel biomarkers for disease progression.