High precision two-step calibration method for the fish-eye camera

Research on the evolution of movement difficulty of competitive aerobics based on digital image processing

Competitive aerobics is a sports project which combines music, aerobics, difficulty and performance as the whole, and takes health, strength and beauty as its movement characteristics. Competitive aerobics is one of the sports that is dominated by skills, and the technical requirements are higher. Through the analysis of the existing literature, the current research on the difficulty of aerobics is only in the general qualitative description and experience summary. So far, there is no comprehensive analysis of the evolution of the competitive gymnastics articles, in the theoretical aspects of the study which is more general, limited. In this work, the method of digital image processing is used to focus on the evolution of the difficulty of aerobics. Combining the rules of the international competitive aerobics competition in each cycle, this work analyzes the statistical data of the movement difficulty of the aerobics championships, discusses the difficulty of aerobics development and evolution process, from summing up the characteristics of the development of difficult movements,the development trend of difficult movements of competitive aerobics is scientifically predicted.

Distorted pinhole camera modeling and calibration

Camera modeling and calibration are essential tasks in modern optics. Conventionally, the pinhole model is adopted with a further extension for lens distortion. However, pinhole and distortion models are mutually dependent; thus, the standard approach induces systematic camera calibration errors. This research presents a unifying distorted pinhole camera model that includes a telecentric, distortion-free pinhole, and radial lens distortion as particular cases. An iterative calibration method based on the derived distorted pinhole model is proposed, and experimental evaluation by calibrating a camera with high radial distortion is performed. The calibration results are compared with the standard and fisheye models using a well-known commercial camera calibrator software. The proposed method outperforms the standard model and achieves accuracy comparable to the fisheye model, and the proposed approach is a versatile and accurate tool for diverse optical metrology applications.

Pre-flight calibration of a multi-angle polarimetric satellite sensor directional polarimetric camera

The directional polarimetric camera (DPC), developed by Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Science, is a satellite sensor used to observe the polarization and directionality of the earth's reflectance. It acquires the two-dimensional image of the earth with a large field of view (118.74°) and a high spatial resolution (3.3 km) in 8 spectral bands. The first DPC was successfully launched onboard the GaoFen-5 satellite in May 2018, subject to the Chinese high-resolution earth observation program. In this paper, a set of systematic and complete pre-flight calibrations of the DPC are proposed to ensure the effective characterization for in-flight calibration, so as to ensure the accuracy of DPC measured radiation polarization data and the reliability of inversion results. Since the geometric calibration method of the DPC has been presented in an early companion paper [Appl. Opt. 59 226 (2020)], this paper will not introduce it in detail. Instead, the geometric calibration results of each spectral band together with a discussion on the origin of differences between spectral bands are analyzed, and the error analysis of the method is conducted. The results of the DPC geometric calibration is that the residuals of all spectral bands are less than 0.1 pixel. For radiometric calibration, the radiometric models of non-polarized bands and polarized bands are derived in detail, respectively, and the specific calibration methods with error analysis, equipment, and main results with their related accuracies for each parameter of the radiometric models are described. To verify the accuracy of calibration parameters, a series of polarization detection accuracy verification experiments based on a non-polarized radiation source, a polarizing system, and a natural scene were carried out. The experimental results show that the maximum deviation of degree of polarization between the set values of the polarizing system and measured values of the DPC at the corresponding positions of four field of view angles of 0, 15, 30, and 45 degrees of each polarized spectral band is 0.009, 0.004, and 0.003, respectively. The average error in measuring the degree of polarization of a non-polarized light source by all pixels in the three polarized bands is 0.0043, 0.0046, and 0.0037, respectively. And the relative deviations of each field of view are within 0.020 when the DPC and CE318N simultaneously measure the DoLP of sky. All of these prove the effectiveness of the pre-flight calibration.

Geometric calibration method based on a two-dimensional turntable for a directional polarimetric camera

The directional polarimetric camera (DPC) is a polarization sensor with ultra-wide-angle and low-distortion imaging characteristics. Geometric calibration is usually the first essential step before remote sensing satellites are launched. In this paper, a geometric calibration method based on a two-dimensional turntable and a rotation matrix with high precision, simple operation, and wide application range is proposed for the directional polarimetric camera. Instead of precisely adjusting the position of the sensor on the turntable, the method effectively eliminates the errors caused by the mechanical axis of the turntable and the optical axis of the sensor not being adjusted to the same direction through the rotation transformation of the coordinate system. The geometric calibration experiments of the directional polarimetric camera were carried out with the method of Chen et al. [Optik121, 486 (2010)10.1016/j.ijleo.2008.08.004OTIKAJ0030-4026] and the proposed method. The experimental results showed the calibration residual of the proposed method was less than 0.1 pixel while Chen's method was 0.3 pixel. The mean reprojection error and root mean square error of the proposed method were reduced to 0.06352 pixel and 0.06961 pixel, respectively. The geometric calibration parameters obtained by the proposed method were used for geometric correction of the in-orbit images of the DPC, and the results also prove the effectiveness and superiority of the proposed method.

Imaging systems and applications

Imaging systems have numerous applications in industrial, military, consumer, and medical settings. Assembling a complete imaging system requires the integration of optics, sensing, image processing, and display rendering. This issue features original research ranging from fundamental theories to novel imaging modalities and provides a systems perspective to imaging.