Computer Optics

493-500

Authors: V.V. Kotlyar, A.A. Kovalev, A.P. Porfirev

In contrast to the orbital angular momentum (OAM), which is conserved on free space propagation, the topological charge (TC) of a paraxial optical vortex (OV) is not conserved in the general case. Here, we investigate a Gaussian beam with a fractional TC in the original plane and demonstrate both theoretically and numerically how the TC changes in the course of propagation. Depending on the proximity of the topological charge to an even or odd integer number, an optical vortex with the original fractional TC is shown to behave in a number of different ways. For simple OVs (Laguerre-Gaussian or Bessel-Gaussian modes), TC is conserved both in propagation and after weak phase distortions. An experiment shows that when scattered by a random phase screen, the integer TC of an OV is conserved right up to a random phase variation of π. Therefore, in the case of weak turbulences, it is expedient to measure a discretely varying TC instead of a continuously varying OAM.

510-518

Authors: V.V. Kotlyar, A.A. Kovalev

Here we theoretically obtain values of the topological charge (TC) for vortex laser beams devoid of radial symmetry: asymmetric Laguerre-Gaussian (LG) beams, Bessel-Gaussian (BG) beams, Kummer beams, and vortex Hermite-Gaussian (HG) beams. All these beams consist of conventional modes, namely, LG, BG, or HG modes, respectively. However, all these modes have the same TC equal to that of a single constituent mode n. Orbital angular momenta (OAM) of all these beams, normalized to the beam power, are different and changing differently with varying beam asymmetry. However, for arbitrary beam asymmetry, TC remains unchanged and equals n. Superposition of just two HG modes with the adjacent numbers (n, n+1) and with the phase retardation of (pi)/2 yields a modal beam with the TC equal to – (2n+1). Numerical simulation confirms the theoretical predictions.

533-539

Authors: V.A. Burdin, A.V. Bourdine, O.Yu. Gubareva

This paper presents the results of an analysis of the necessary propagation conditions in a step-index optical fiber with a Kerr nonlinearity of two modes, LP01 and LP11, during the transmission of high-power optical pulses. All results were obtained by solving a system of two nonlinear equations for these modes, obtained by the Gauss approximation method, and the subsequent use of a procedure for refining estimates using the mixed finite elements method. The necessary conditions are determined, estimates of the boundaries for the range of normalised frequencies for which they are fulfilled are obtained, and an approximate formula is proposed for estimating the upper limit of this range.

547-551

Authors: S.A. Shoydin

A method for the synthesis of holograms that reconstruct a 3D image using two 2D images, including a topographic map of the surface of a 3D object and photographs of the texture of its surface obtained using coherent and incoherent radiation is proposed. The method is suitable for transmitting information about a 3D object via a communication channel at a distance and subsequent synthesis of holograms at a distance from the holography object. It can be used in augmented reality devices, when creating holographic cameras and 3D video cameras, in 3D projectors and microscopes, devices with a synthesized aperture. The proposed method for the remote hologram synthesis is suitable for reproducing 3D holographic images of distant objects at different parts of the electromagnetic spectrum. Examples of 3D image restoration in the infrared spectral range are given. The method is also suitable for the synthesis of holograms in the UV, THz, and even radio range.

561-567

Authors: A.G. Nalimov, S.S. Stafeev

A force and a torque exerted on an elliptical dielectric particle in the focus of a spherical circularly polarized laser beam are considered. The numerical simulation is conducted using a diffraction field obtained by an FDTD method, with the force and torque derived using a Maxwell’s stress tensor. It is shown that an optical torque is exerted on the center of an elliptical particle put in the focus of a circularly polarized spherical wave, making it rotate around the optical axis. The rotation occurs when the elliptical microparticle is situated in a transverse plane to the optical axis. When shifting the ellipsoid from the optical axis, an optical trapping force appears that prevents its displacement, meaning that the particle finds itself in an optical trap on the optical axis.

578-581

Authors: S.V. Karpeev, V.V. Podlipnov, N.A. Ivliev, S.N. Khonina

The possibility of constructing a near-infrared atmospheric optical communication system based on a pair of media converters of a signal format 100Base-TX / 1000BASE-T to format 1000BASE-SX / LX with SFP transceivers DEM-310GT was experimentally investigated. The FAN-OUT TUBING FTB900 SN-Y4 fiber cable connector, coming from the receiving radiation collimator for matching with the DEM-310GT transceiver, was modified. The transmitting radiation collimator is supplemented by a spiral phase plate to form a vortex beam. The influence of atmospheric influence on the data rate is analyzed.

589-595

Authors: Y.V. Vizilter, V.S. Gorbatsevich, A.S. Moiseenko

Facial landmark detection is an important sub-task in solving a number of biometric facial recognition tasks. In face recognition systems, the construction of a biometric template occurs according to a previously aligned (normalized) face image and the normalization stage includes the task of finding facial keypoints. A balance between quality and speed of the facial keypoints detector is important in such a problem. This article proposes a CNN-based one-stage detector of faces and keypoints operating in real time and achieving high quality on a number of well-known test datasets (such as AFLW2000, COFW, Menpo2D). The proposed face and facial landmarks detector is based on the idea of a one-stage SSD object detector, which has established itself as an algorithm that provides high speed and high quality in object detection task. As a basic CNN architecture, we used the ShuffleNet V2 network. An important feature of the proposed algorithm is that the face and facial keypoint detection is done in one CNN forward pass, which can significantly save time at the implementation stage. Also, such multitasking allows one to reduce the percentage of errors in the facial keypoints detection task, which positively affects the final face recognition algorithm quality.

606-617

Authors: I.G. Palchikova, E.S. Smirnov, O.A. Barinova, I.V. Latyshov, V.A. Vasiliev, A.V. Kondakov

We discuss aspects of the use and possibilities provided by three-color colorimeters or digital cameras in problems of detecting small color differences by computer vision methods. The spectral dependence of the total color differences between pairs of visually indiscernible monochromatic stimuli is experimentally revealed. An experimental setup based on the UM-2 monochromator is created for producing a digital atlas of monochromatic stimuli at 1-nm increments. The atlas serves to test the color gamut and color differentiation of cameras. It is experimentally shown that in the visible spectral range a color difference of 3 units is detected by pairs of stimuli that are unevenly distributed across the spectrum and differ in wavelengths from 1 to 6 nm. The capabilities of computer vision are tested on the examples of identifying additional texts during a technical and forensic examination of documents. A new algorithm is developed for finding and quantitatively characterizing color difference of inserts based on a digital image of the inscription. In the algorithm, the objective analysis of the image is divided into a block of color segmentation and that of color tone and color difference assessment. With such an approach, the color segmentation block performs preprocessing functions, making a border map for the classes with different colors for the subsequent calculations. The Otsu method of optimal global threshold transformation is for the first time applied to a problem of image segmentation by color saturation. The trial of the algorithm confirms its efficiency in the solution of expert tasks.

627-635

Authors: A.M. Belov, A.Y. Denisova

Earth remote sensing data fusion is intended to produce images of higher quality than the original ones. However, the fusion impact on further thematic processing remains an open question because fusion methods are mostly used to improve the visual data representation. This article addresses an issue of the effect of fusion with increasing spatial and spectral resolution of data on thematic classification of images using various state-of-the-art classifiers and features extraction methods. In this paper, we use our own algorithm to perform multi-frame image fusion over optical remote sensing images with different spatial and spectral resolutions. For classification, we applied support vector machines and Random Forest algorithms. For features, we used spectral channels, extended attribute profiles and local feature attribute profiles. An experimental study was carried out using model images of four imaging systems. The resulting image had a spatial resolution of 2, 3, 4 and 5 times better than for the original images of each imaging system, respectively. As a result of our studies, it was revealed that for the support vector machines method, fusion was inexpedient since excessive spatial details had a negative effect on the classification. For the Random Forest algorithm, the classification results of a fused image were more accurate than for the original low-resolution images in 90% of cases. For example, for images with the smallest difference in spatial resolution (2 times) from the fusion result, the classification accuracy of the fused image was on average 4% higher. In addition, the results obtained for the Random Forest algorithm with fusion were better than the results for the support vector machines method without fusion. Additionally, it was shown that the classification accuracy of a fused image using the Random Forest method could be increased by an average of 9% due to the use of extended attribute profiles as features. Thus, when using data fusion, it is better to use the Random Forest classifier, whereas using fusion with the support vector machines method is not recommended.

646-652

Authors: A.A. Borodinov

The paper considers a problem of determining the user preferred stops in a public transport recommender system. The effectiveness of using various machine learning methods to solve this problem in a system of personalized recommendations is compared, including a support vector method, a decision tree, a random forest, AdaBoost, a k-nearest neighbors algorithm, and a multi-layer perceptron. The described traditional methods of machine learning are also compared with the method proposed herein and based on an estimate calculation algorithm. The efficiency and the effectiveness of the proposed method are confirmed in the work.

660-664

Authors: W.H. Yang

In order to resist network malicious attacks, this paper briefly introduced the network intrusion detection model and K-means clustering analysis algorithm, improved them, and made a simulation analysis on two clustering analysis algorithms on MATLAB software. The results showed that the improved K-means algorithm could achieve central convergence faster in training, and the mean square deviation of clustering center was smaller than the traditional one in convergence. In the detection of normal and abnormal data, the improved K-means algorithm had higher accuracy and lower false alarm rate and missing report rate. In summary, the improved K-means algorithm can be applied to network intrusion detection.

671-679

Authors: D.A. Shepelev, V.P. Bozhkova, E.I. Ershov, D.P. Nikolaev

This paper considers methods for simulating color underwater images based on real terrestrial images. Underwater image simulation is widely used for developing and testing methods for improving underwater images. A large group of existing methods uses the same deterministic image transformation model ignoring the presence of noise in images. The paper demonstrates that this significantly affects the overall quality of underwater images simulation. It is shown both theoretically and numerically that the accuracy of the signal-to-noise ratio of underwater images simulated using a deterministic transformation decreases with increasing distance to the object. To solve this problem, a new model of image transformation for simulating underwater images based on terrestrial images is proposed, which considers the presence of noise in the image and is compatible with all simulating methods from the group under consideration. The paper presents the results of the simulation based on the existing and proposed models, showing that at long distances, the new results are better consistent with real data.