Distortion Parameters Research Articles

CALIBRATION OF SMARTPHONE’S REAR DUAL CAMERA SYSTEM

This paper aims to calibrate smartphone’s rear dual camera system which is composed of two lenses, namely; wide-angle lens and telephoto lens. The proposed approach handles large sized images. Calibration was done by capturing 13 photos for a chessboard pattern from different exposure positions. First, photos were captured in dual camera mode. Then, for both wide-angle and telephoto lenses, image coordinates for node points of the chessboard were extracted. Afterwards, intrinsic, extrinsic, and lens distortion parameters for each lens were calculated. In order to enhance the accuracy of the calibration model, a constrained least-squares solution was applied. The applied constraint was that the relative extrinsic parameters of both wide-angle and telephoto lenses were set as constant regardless of the exposure position. Moreover, photos were rectified in order to eliminate the effect of lens distortion. For results evaluation, two oriented photos were chosen to perform a stereo-pair intersection. Then, the node points of the chessboard pattern were used as check points.

The influence of visual distortion on face recognition

A person's ability to recognise familiar faces is critical to their participation in many aspects of society. Following an acquired brain injury or retinal disease, however, faces can appear distorted, a phenomenon known as prosopometamorphopsia. Although case reports have described a variety of changes in the appearance of faces during prosopometamorphopsia, the influence of the disorder on face recognition has not been rigorously investigated. In the present report, we quantify how well healthy observers can recognise familiar faces that have been distorted using a parametric model of prosopometamorphopsia. Our results reveal that face recognition varies systematically with the parameters of visual distortion, which, importantly, interact with the size of the face in a nonlinear but highly predictable manner. Our findings demonstrate that prosopometamorphopsia can lead to a surprising range of changes in the appearance of faces. The impact of visual distortion on face recognition thus depends critically on the distance at which the face is viewed, which is likely to change across social and clinical contexts.

COMBINED NEURAL NETWORK METHOD FOR DETERMINING THE BRILLOUIN SPECTRUM MAXIMUM IN DISTRIBUTED FIBER-OPTIC SENSORS

Distributed fiber-optic sensors are becoming an increasingly common solution for monitoring and diagnosing extended information transmission lines, industrial devices, buildings and devices. One of the directions – Brillouin reflectometry, which allows diagnosing a fiber line for changes in ambient temperature or mechanical deformation, is becoming increasingly popular for engineers and researchers. However, modern standards impose increasingly strict requirements on diagnostic systems in terms of the accuracy of determined parameters. For Brillouin reflectometry, where the value of the environmental parameters is determined by the position of the maximum of the Brillouin gain spectrum, the task of more accurately determining this maximum becomes the main one. The paper considers modern computer-computational methods for detecting the maximum of the Brillouin gain spectrum in an optical fiber. The authors note that imperfections in the shape of the optical spectrum, such as the signal-to-noise ratio, as well as possible digital defects that occur during digitization, can significantly impair the accuracy of the system. The authors consider three approaches to detecting the maximum of the spectrum: the classical method of Lorentz curve fitting, the method of cross-correlation with the ideal Lorentzian function, as well as the method of inverse correlation developed by the authors earlier. To combine the results of the work of the three methods, a neural network model was developed that accepts the input data of each method, together with the parameters of noise and distortion of the spectrum. The model is presented in the form of a four-layer perceptron with two hidden layers. As a result, the authors achieved an increase in the accuracy of determining the position of the maximum of the spectrum by 10% on the model data.

Analysis of Errors in Active Power and Energy Measurements Under Random Harmonic Distortion Conditions

Abstract As harmonic distortion of voltage and current is reality in the power system, the need for accurate measurement of electrical power and energy goes beyond the instruments’ specifications and calibration procedures regarding pure sine wave signals. Several international standards and recommendations provide test signals for examination of electricity meters under non-sinusoidal conditions, however, not all of the test signal parameters’ possible states are faithfully represented in those documents. Because the high order harmonics may possess random amplitudes and phase shifts in relation to components at fundamental frequency, it is important that the meter’s performance is verified with random waveforms as well. The non-linear dependence between the measured power/energy and the phase shifts, both between fundamental and harmonic components, provides additional complexity of such an analysis. Simple test signals, which are in accordance with the standards’ demands and propositions, are used for determination of the measurement error in case of different harmonic distortion parameter change. In order for a general error function for any measurement device to be determined, mathematical modelling, regarding the results from multiple tests, is performed. The mathematical model presents a strong dependence between a single component’s phase shifts and a meter’s error and it provides a systematization of all signal parameters’ influence on the measurement accuracy.

Camera Self-Calibration with GNSS Constrained Bundle Adjustment for Weakly Structured Long Corridor UAV Images

Camera self-calibration determines the precision and robustness of AT (aerial triangulation) for UAV (unmanned aerial vehicle) images. The UAV images collected from long transmission line corridors are critical configurations, which may lead to the “bowl effect” with camera self-calibration. To solve such problems, traditional methods rely on more than three GCPs (ground control points), while this study designs a new self-calibration method with only one GCP. First, existing camera distortion models are grouped into two categories, i.e., physical and mathematical models, and their mathematical formulas are exploited in detail. Second, within an incremental SfM (Structure from Motion) framework, a camera self-calibration method is designed, which combines the strategies for initializing camera distortion parameters and fusing high-precision GNSS (Global Navigation Satellite System) observations. The former is achieved by using an iterative optimization algorithm that progressively optimizes camera parameters; the latter is implemented through inequality constrained BA (bundle adjustment). Finally, by using four UAV datasets collected from two sites with two data acquisition modes, the proposed algorithm is comprehensively analyzed and verified, and the experimental results demonstrate that the proposed method can dramatically alleviate the “bowl effect” of self-calibration for weakly structured long corridor UAV images, and the horizontal and vertical accuracy can reach 0.04 m and 0.05 m, respectively, when using one GCP. In addition, compared with open-source and commercial software, the proposed method achieves competitive or better performance.

Transdimensional Bayesian inversion of magnetotelluric data in anisotropic layered media with galvanic distortion correction

SUMMARYPresence of electrical anisotropy in the lithosphere can provide useful constraints on regional structure patterns and dynamics of tectonic processes, and they can be imaged by magnetotelluric (MT) data. However, Inversion of MT data for anisotropic structures using standard gradient-based approaches requires subjective choices of model regularization for constraining structure and anisotropy complexity. Furthermore, the ubiquitous presence of galvanic distortion due to small-scale near-surface conductivity inhomogeneities prevents accurate imaging of subsurface structures if ignored or not properly removed. Here, we present a transdimensional Bayesian approach for inverting MT data in layered anisotropic media. The algorithm allows flexible model parametrization, in which both the number of layers and model parameters of each layer are treated as unknowns. In this manner, the presence or absence of anisotropy within the layers, as well as the level of model complexity, is determined adaptively by the data. In addition, to account for the effects of galvanic distortion, three frequency-independent distortion parameters resulting from the distortion decomposition are treated as additional variables during the inversion. We demonstrate the efficiency of the algorithm to resolve both isotropic and anisotropic structures with synthetic and field MT data sets affected by galvanic distortion effects. The transdimensional inversion results for the field data are compatible with results from previous studies, and our results improve the constraints on the magnitude and the azimuth (i.e. most conductive direction) of electrically anisotropic structures. For practical applications, the validity of 1-D anisotropic approximation should be first tested prior to the use of our approach. Otherwise it may produce spurious anisotropic structures due to the inapplicability of the anisotropic 1-D inversion for MT data affected by 2-D or 3-D electrical resistivity structures.

Parametric Doppler correction analysis for wayside acoustic bearing fault diagnosis

Wayside acoustic system plays a crucial role in monitoring and diagnosing the status of train wheel bearings. However, due to the signal distortion caused by Doppler effect, the diagnosis accuracy will be seriously disturbed. In this manner, this paper proposes a model-driven Doppler distortion self-tuning method in theory, named as parametric Doppler correction analysis (PDCA). Different from traditional methods, such as instantaneous frequency tracking and Doppler distortion sparse representation, the proposed method aims to abstractly construct a physical model of acoustic signal distortion propagation based on Morse acoustic theory, where the acoustic forward propagation model and reverse reconstruction model are simultaneously built. The scheme consists of four basic steps. Firstly, the physical model with amplitude modulation operator and frequency shift operator is described for the distortion process. Secondly, the pseudo transition signal with the characteristics of energy accumulation and no distortion is obtained via a construction of frequency rearrangement operator and amplitude demodulation operator. Then, pseudo Doppler correction (PDC) is presented to solve the frequency distortion of the received signal, where a high energy accumulation for frequency distribution is designed as optimization function. Especially, quasi Newton algorithm L-BFGS is used to realize the adaptive learning for distortion parameters. Finally, through time-domain interpolation resampling (TIR) technique, the corrected signal can be analytically reconstructed with the optimal parameters. Applying the PDCA scheme to simulated signals and experimental signals, its validity is verified. The comparison with the instantaneous frequency ridge extraction approach further indicates the proposed model-driven method can reach a more accurate correction result in a faster and adaptive process.

Temperature-dependent structure and magnetization of YCrO3 compound

We have grown a YCrO3 single crystal by the floating-zone method and studied its temperature-dependent crystalline structure and magnetization by x-ray powder diffraction and PPMS DynaCool measurements. All diffraction patterns were well indexed by an orthorhombic structure with space group of Pbnm (No. 62). From 36 K to 300 K, no structural phase transition occurs in the pulverized YCrO3 single crystal. The antiferromagnetic phase transition temperature was determined as T N = 141.58(5) K by the magnetization versus temperature measurements. We found weak ferromagnetic behavior in the magnetic hysteresis loops below T N. Especially, we demonstrated that the antiferromagnetism and weak ferromagnetism appear simultaneously upon cooling. The lattice parameters (a, b, c, and V) deviate downward from the Grüneisen law, displaying an anisotropic magnetostriction effect. We extracted temperature variation of the local distortion parameter Δ. Compared to the Δ value of Cr ions, Y, O1, and O2 ions show one order of magnitude larger Δ values indicative of much stronger local lattice distortions. Moreover, the calculated bond valence states of Y and O2 ions have obvious subduction charges.

3D Behaviour of Buildings due to Tunnel Induced Ground Movement

Ground subsidence from tunnel excavation below existing buildings may result in building distortion and develop structural damage. Previous case histories have shown that buildings may deform three-dimensionally when the tunnel alignment is orientated to the building facade. The authors incorporated a three-dimensional distortion parameter called twist into damage assessment by extending the current beam model to three dimensions. In this study, the new method is reviewed, and the concepts of the local and global twists are discussed. Results of a 3D Finite Element (FE) parametric study of global and local twist deformations of buildings due to tunnel-induced ground movement are compared in temporary and permanent cases during and after the construction of the tunnel. To investigate the behaviour of a twisted building, varying building stiffness, building geometry, and orientation angle are considered in the analyses. Comparison of the global and local twist shows that the global twist is not always the maximum twist during or after excavation of the tunnel. However, because of the temporary nature of the local twist, the global twist is still considered more critical than the local twist in terms of damage to the building. A new modification factor for the twist for different building stiffness factor is being proposed in the form of design graph. The design graph is included in the current three-stage procedure for assessing potential building damage. The modified procedure is used to predict the performance of a case study building affected by tunnel construction.

DQN-based gradual fisheye image rectification

Fisheye image rectification is a classic and important task in the computer vision area, which is generally treated as a pre-processing step in many application scenarios. Most of the existing fisheye image rectification methods focused mainly on building a direct (one-step) projection relationship between fisheye images and corrected images. Although these methods have achieved impressive performance, they depended heavily on data distribution and cannot work well on images whose distortion parameters are out of range. To address this issue, we propose a multi-step gradual image rectification scheme. In particular, we treat the fisheye image rectification problem as one Markov Decision Process and employ a widely-used deep reinforcement learning method (i.e., Deep Q-Network) to solve the problem. In addition, we build a new large-scale fisheye image dataset to evaluate our method, which contains 50,000 training images and 5000 test images. Experimental results show the proposed method can better handle images with a wide range of distortion.

Understanding distortions of inorganic substructures in chloridobismuthates(III)

The molar ratio variations of organic and inorganic reactants of chloridobismuthates(III) with N,N-dimethylethane-1,2-diammonium, [(CH3)2NH(CH2)2NH3]2+, and N,N,N′,N′-tetramethylguanidinium, [NH2C{N(CH3)2}2]+, cations lead to the formation of four different products, namely, tris(N,N-dimethylethane-1,2-diammonium) bis[hexachloridobismuthate(III)], [(CH3)2NH(CH2)2NH3]3[BiCl6]2 (1), catena-poly[N,N-dimethylethane-1,2-diammonium [[tetrachloridobismuthate(III)]-μ-chlorido]], {[(CH3)2NH(CH2)2NH3][BiCl5]} n (2), tris(N,N,N′,N′-tetramethylguanidinium) tri-μ-chlorido-bis[trichloridobismuthate(III)], [NH2C{N(CH3)2}2]3[Bi2Cl9] (3), and catena-poly[N,N,N′,N′-tetramethylguanidinium [[dichloridobismuthate(III)]-di-μ-chlorido]], {[NH2C{N(CH3)2}2][BiCl4]} n (4). The hybrid crystals 1–4, containing relatively large but different organic cations, are composed of four distinct anionic substructures. They are built up from isolated [BiCl6]3− octahedra in 1, from face-sharing bioctahedral [Bi2Cl9]3− units in 3, from polymeric corner-sharing {[BiCl5]2−} n chains in 2 and from edge-sharing {[BiCl4]−} n chains in 4. The distortions shown by the single [BiCl6]3− polyhedra in 1–4 are associated with intrinsic interactions within the anionic substructures and the organic...inorganic substructures interactions, namely, N/C—H...Cl hydrogen bonds. The first factor is the stronger, which is evident in comparison of the experimentally determined geometrical and calculated distortion parameters for the isolated octahedron in 1 to the more complex inorganic substructures in 2–4. The formation of N—H...Cl hydrogen bonds, in terms of their number and strength, is favoured for 1 and 3 containing relatively easily accessed hydrogen-bond acceptors of isolated [BiCl6]3− and [Bi2Cl9]3− units. The studies of the deviations from regularity of the [BiCl6]3− octahedra within inorganic substructures were supported by a survey of the Cambridge Structural Database, which confirmed the role played by different factors in the variations in geometry of the inorganic anions.

3D heat flow effects in the imaging of subsurface graphical features in semi-transparent media by pulsed thermography

Pulsed thermography has proven to be a useful tool to detect subsurface features in ancient bookbindings and, in particular, to provide the IR image of texts buried beneath the end-leaves of the books. In this paper the theory is presented to analyze the influence of the geometrical and physical parameters involved in the processes leading to the distortion in the IR image of the detected buried graphical features. The distortion is mainly due to the lateral diffusion of the heat generated at the ink feature after the absorption of an excitation light. A comprehensive analysis taking into account the three dimensional heat diffusion process, in an optically semi-transparent medium, is considered. Numerical results are reported showing the behavior of the contrast and of a distortion parameter of the buried inked feature detected by the IR imaging in the various considered cases.

Optimization of stereo calibration parameters for the binocular camera based on improved Beetle Antennae Search algorithm

For binocular cameras, aiming at the low precision of traditional stereo calibration methods for binocular cameras, a Beetle Antennae Search (BAS) algorithm based on binocular parallel polar line constraint was proposed to improve the calibration accuracy. The internal parameter matrix and distortion parameter matrix of the left and right cameras of the binocular camera were first calculated by using the MATLAB calibration toolbox. Then the stereo calibration parameter matrix of the binocular camera was calculated. Then, using the binocular parallel polar line constraint based on the BAS algorithm establishes the objective function by taking the difference and average values of the vertical coordinates of each checkerboard corner in the left and right images after stereo correction as the objective. The stereo calibration parameters of the binocular camera are further optimized. The results show that the BAS algorithm based on binocular parallel pole constraint is stable, reliable and fast in convergence, which can realize the optimization of stereo calibration parameters of the binocular camera.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe ^III ₄ Fe ^II ₄ } Cubes

Iterative feature detection of a coded checkerboard target for the geometric calibration of infrared cameras

Abstract. The geometric calibration of cameras becomes necessary when images should be undistorted, geometric image information is needed or data from more than one camera have to be fused. This process is often done using a target with a checkerboard or circular pattern and a given geometry. In this work, a coded checkerboard target for thermal imaging cameras and the corresponding image processing algorithm for iterative feature detection are presented. It is shown that, due in particular to the resulting better feature detectability at image borders, lower uncertainties in the estimation of the distortion parameters are achieved.

Structural and optical characterization of alpha-irradiated and chemically etched PM-355 solid state nuclear track detectors before and after solar exposure

PM-355 polymeric solid state nuclear track detectors were studied. Samples were irradiated with alpha particles before and after exposure to sunlight under various seasonal conditions. Track formation and optical characteristics of chemically etched samples were investigated.X-ray diffraction (XRD) analysis showed that the dominant structure of the PM-355 detectors is of an amorphous nature with some degree of crystallinity. Micro strain, distortion density and distortion parameter were calculated from the XRD data, and indicate that the structure was modified after alpha irradiation and solar exposure. There was a tendency in the structure towards crystallinity.Some optical properties of PM-355 detectors were studied using Ultraviolet–Visible absorption spectroscopy. The absorption edge was detectable in all samples. The direct band gap decreased first and then subsequently increased again. The fluorescence spectra of alpha irradiated and solar exposed PM-355 polymer detectors after chemical etching showed three dominant peaks at wavelengths 327, 418 and 465 nm, respectively. The changes in the optical properties can be used to detect the effect of alpha and ultraviolet irradiations. The variation of the optical band gap, fluorescence spectra and/or track diameters can be used as a detection of nuclear radiation.

Cosmic voids and induced hyperbolicity. III. Tracing redshift dependence

The currently released datasets of the observational surveys reveal the redshift dependence of the physical features of cosmic voids. We study the void induced hyperbolicity, that is the deviation of the photon beams propagating the voids, taking into account the redshift dependence of the void size indicated by the observational surveys. The cumulative image distortion parameter is obtained for the case of a sequence of variable size voids and given underdensity parameters. The derived formulae applied along with those of redshift distortion ones, enable one to trace the number and the physical parameters of the line-of-sight voids from the analysis of the distortion in the galactic surveys.}

Microstructure, distortion characteristics and mechanical behaviour of NiB modified 90W-6Ni-4Co heavy alloys

In this work, the effect of NiB on densification, phase, microstructure, distortion and mechanical properties of conventionally sintered ternary 90W-6Ni-4Co heavy alloy has been investigated without altering (Ni+NiB)/Co ratio. No intermetallic phase was detected in the heavy alloys upon addition of NiB. Instead, the partial and complete exchange of Ni with NiB in 90W-6Ni-4Co has elicited relatively better densification (>99% theoretical), higher bulk hardness (HV3 ~ 389–396 VHN), higher hardness of matrix (~352 HV0.025) when the alloys were sintered at 1500 °C. In addition to W grains and matrix, the completely NiB-substituted heavy alloy (90W-6NiB-4Co) sintered at 1500 °C exhibits the occurrence of W-rich third phase which contains ~75 wt% of W. Although the samples prevented slumping at 1475 °C, elephant foot formation was found inevitable in the base composition (90W-6Ni-4Co) when sintering was carried out at 1500 °C. However, the decreased distortion parameter (from 24.8 to 8.5) with optimal NiB addition affirms the enhanced shape retention capability of 90W-3Ni-3NiB-4Co and 90W-6NiB-4Co heavy alloys. Room temperature compression test of WHAs sintered at 1475 °C was performed at a fixed strain rate of 0.1 s-1. No crack formation was observed in NiB containing samples up to 40% deformation. Moreover, the systematic addition of 3–6 wt% NiB resulted in lower coefficient of thermal expansion of NiB-containing heavy alloys in the temperature range of 400–600 °C.

First high resolution study of the pentad bending bands of deuterated silane: Energy structure of the (0200), (0101) and (0002) vibrational states of [formula omitted]SiD[formula omitted], [formula omitted]SiD[formula omitted] and [formula omitted]SiD[formula omitted

The infrared spectra of SiD4 in natural abundance were measured in the region of 350–2050 cm−1 with a Bruker IFS 125HR Fourier transform interferometer at an optical resolution of 0.0021 and 0.0016 cm−1 and analyzed. Not less than 6490 transitions with Jmax = 33 were assigned for the first time to the bands 2ν4, ν2+ν4, and 2ν2 of the 28SiD4 molecule. Numerous “hot” dyad–pentad transitions (in general, 5545 “hot” transitions) were also assigned for the first time in the region of 600–760 cm−1. Rotational, centrifugal distortion, tetrahedral splitting, and interaction parameters for the (0002,F2), (0002,E), (0002,A1), (0101,F2), (0101,F1), (0200,A1) and (0200,E) vibrational states were determined from the fit of experimental line positions. The obtained set of 69 fitted parameters reproduces the initial experimental data with an accuracy of drms=3.12×10−4 cm−1 for the 6490 “cold” transitions and drms=2.33×10−4 cm−1 for the 5545 “hot” transitions. Results of the analogues analysis for the 29SiD4 and 30SiD4 isotopologues with 403/136 “cold” and 171/99 “hot” assigned transitions are presented also.

Evaluation of Cyclic Amides as Activating Groups in N-C Bond Cross-Coupling: Discovery of N-Acyl-δ-valerolactams as Effective Twisted Amide Precursors for Cross-Coupling Reactions.

The development of efficient methods for facilitating N-C(O) bond activation in amides is an important objective in organic synthesis that permits the manipulation of the traditionally unreactive amide bonds. Herein, we report a comparative evaluation of a series of cyclic amides as activating groups in amide N-C(O) bond cross-coupling. Evaluation of N-acyl-imides, N-acyl-lactams, and N-acyl-oxazolidinones bearing five- and six-membered rings using Pd(II)-NHC and Pd-phosphine systems reveals the relative reactivity order of N-activating groups in Suzuki-Miyaura cross-coupling. The reactivity of activated phenolic esters and thioesters is evaluated for comparison in O-C(O) and S-C(O) cross-coupling under the same reaction conditions. Most notably, the study reveals N-acyl-δ-valerolactams as a highly effective class of mono-N-acyl-activated amide precursors in cross-coupling. The X-ray structure of the model N-acyl-δ-valerolactam is characterized by an additive Winkler-Dunitz distortion parameter Σ(τ+χN) of 54.0°, placing this amide in a medium distortion range of twisted amides. Computational studies provide insight into the structural and energetic parameters of the amide bond, including amidic resonance, N/O-protonation aptitude, and the rotational barrier around the N-C(O) axis. This class of N-acyl-lactams will be a valuable addition to the growing portfolio of amide electrophiles for cross-coupling reactions by acyl-metal intermediates.