Computer Optics

337-346

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

Using the Richards-Wolf formalism, we obtain general expressions for all components of the electric and magnetic strength vectors near the sharp focus of an optical vortex with the topological charge m and nth-order azimuthal polarization. From these equations, simple consequences are derived for different values of m and n. If m = n > 1, there is a non-zero intensity on the optical axis, like the one observed when focusing a vortex-free circularly polarized light field. If n = m + 2, there is a reverse flux of light energy near the optical axis in the focal plane. The derived expressions can be used both for simulating the sharp focusing of optical fields with the double singularity (phase and polarization) and for a theoretical analysis of focal distributions of the intensity and the Poynting vector, allowing one to reveal the presence of rotational symmetry or the on-axis reverse energy flux, as well as the focal spot shape (a circle or a doughnut).

356-367

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

Here we study three different types of astigmatic Gaussian beams, whose complex amplitude in the Fresnel diffraction zone is described by the complex argument Hermite polynomial of the order (n, 0). The first type is a circularly symmetric Gaussian optical vortex with and a topological charge n after passing through a cylindrical lens. On propagation, the optical vortex "splits" into nfirst-order optical vortices. Its orbital angular momentum per photon is equal to n. The second type is an elliptical Gaussian optical vortex with a topological charge n after passing through a cylindrical lens. With a special choice of the ellipticity degree (1: 3), such a beam retains its structure upon propagation and the degenerate intensity null on the optical axis does not “split” into n optical vortices.Such a beam has fractional orbital angular momentum not equal to n. The third type is the astigmatic Hermite-Gaussian beam (HG) of order (n, 0), which is generated when a HG beam passes through a cylindrical lens. The cylindrical lens brings the orbital angular momentum into the original HG beam. The orbital angular momentum of such a beam is the sum of the vortex and astigmatic components, and can reach large values (tens and hundreds of thousands per рhoton). Under certain conditions, the zero intensity lines of the HG beam "merge" into an n-fold degenerate intensity null on the optical axis, and the orbital angular momentum of such a beam is equal to n. Using intensity distributions of the astigmatic HG beam in foci of two cylindrical lenses, we calculate the normalized orbital angular momentum which differs only by 7 % from its theoretical orbital angular momentum value (experimental orbital angular momentum is –13,62, theoretical OAM is –14.76).

376-384

Authors: V.S. Vasilyev, A.I. Kapustin, R.V. Skidanov, V.V. Podlipnov,N.A. Ivliev,S.V. Ganchevskaya

We described an experiment on passing Bessel beams through the atmosphere with heat-trolled flows. We showed that at small distances, while passing through the region with a hot air flow, the Bessel beam can be distorted to a complete loss of the structure, but with further propagation over large distances it completely restores its structure. We also described an experiment with the passage of superpositions of vortex beams through the atmosphere with heat flows and aerosols.

391- 396

Authors: M.S. Kuzmin, V.V. Davydov, S.A. Rogov

A mathematical description of a coherent optical correlator for the multi-raster input of long signals is given. It is shown that such an input makes it possible to reduce the value of false correlation maxima that are generally found at the output of a correlator with a single-raster input. It is shown that false maxima do not appear when processing signals with a thumbtack ambiguity function, allowing one to do without a multi-raster input. The results of the theoretical analysis are confirmed by experiments with chirp signals and M-sequence type signals.

402-411

Authors: A.V. Mingalev, A.V. Belov, I.M. Gabdullin, R.R. Agafonova, S.N. Shusharin

The paper presents a comparative analysis of several methods for recognition of test-object position in a thermal image when setting and testing characteristics of thermal image channels in an automated mode. We consider methods of image recognition based on the correlation image comparison, Viola-Jones method, LeNet classificatory convolutional neural network, GoogleNet (Inception v.1) classificatory convolutional neural network, and a deep-learning-based convolutional neural network of Single-Shot Multibox Detector (SSD) VGG16 type. The best performance is reached via using the deep-learning-based convolutional neural network of the VGG16-type. The main advantages of this method include robustness to variations in the test object size; high values of accuracy and recall parameters; and doing without additional methods for RoI (region of interest) localization.

419-433

Authors: A.A. Egorova ,V.A. Fedoseev

The article discusses semi-fragile digital watermarking systems designed to protect JPEG images against unauthorized changes. These systems allow detecting and locating changes, and some of them are able to restore the original content. Formal schemes describing the procedures for watermark embedding and authentication are given. We consider more than a dozen systems of this type and classify them according to various criteria. We also consider the results of experimental studies of these systems estimating their level of distortions arising from watermark embedding. In addition, we test the systems whether they are able to operate in the semi-fragile way.

446-454

Authors: Afef Bettaieb, Nabila Filali, Taoufik Filali, Habib Ben Aissia

Accurate detection of air bubbles boundaries is of crucial importance in determining the performanceand in the study of various gas/liquid two-phase flow systems. The main goal of this work is edge extraction of air bubbles rising in two-phase flow in real-time. To accomplish this, a fast algorithm based on local variance is improved and accelerated on the GPU to detect bubble contour. The proposed method is robust against changes of intensity contrast of edges and capable of giving high detection responses on low contrast edges. This algorithm is performed in two steps: in the first step, the local variance of each pixel is computed based on integral image, and then the resulting contours are thinned to generate the final edge map. We have implemented our algorithm on an NVIDIA GTX 780 GPU. The parallel implementation of our algorithm gives a speedup factor equal to 17x for high resolution images (1024×1024 pixels) compared to the serial implementation. Also, quantitative and qualitative assessments of our algorithm versus the most common edge detection algorithms from the literature were performed. A remarkable performance in terms of results accuracy and computation time is achieved with our algorithm.

464-473

Authors: S.M. Borzov, M.A. Guryanov, O.I. Potaturkin

The article is devoted to the effectiveness research of methods of controlled spectral and spectral-spatial classification of hyperspectral data. In particular, minimum distance, support vector machine, mahalanobis distance and maximum likelihood methods are considered on the example of vegetative cover types differentiation. Significant attention is paid to studying the dependence of the accuracy of data classification with listed methods on the spectral features number and their selection method. The perspectivity of complex processing of spectral and spatial features, considering the correlation of close pixels, is demonstrated. The experimental results obtained with various methods of forming training sets are presented.

484- 491

Authors: V.A. Fursov, Ye.V. Goshin, K.S. Medvedeva

The article is devoted to the problem of improving the quality of images recorded using lowresolution optical instruments, including diffraction-based cameras. A two-stage image correction technology is proposed. At the first stage, the correction is carried out using a linear FIR filter with a centrally symmetric frequency response in the form of quadratic and exponential functions. The resulting image is then processed with a non-linear filter that performs computer retouching of image areas characterized by a noticeable brightness difference. This procedure is only performed on those pixels in which the absolute value of gradients in different directions is sufficiently high, that is, they are located on the borders of areas with different intensity levels. This allows us to avoid noise amplification in the background, which is typical of traditional filters. The examples of the implementation are provided, showing the possibility of achieving high sharpness and illustrating how the filter can be adjusted by visual perception.

504-506

Authors: V.G. Volostnikov

At first sight, any rotation generates some angular momentum (it is true for a solid body). But these characteristics (rotation and orbital angular momentum) are rather different for optics and mechanics. In optics there are the situation when the rotation is important. On the other hand, there are the cases where the nonzero orbital angular momentum is necessary. The main goal of this article is to investigate a relationship between a rotation under propagation of spiral beam and its angular momentum.