Статьи журнала - Компьютерная оптика
Все статьи: 2382
Determination of the beam waist position for the spin-orbit interaction effect observation
Статья научная
The spin angular momentum and the extrinsic orbital angular momentum of light are associated with the polarization of light and the light propagation trajectory, respectively. Those momenta are interdependent not only in an inhomogeneous or anisotropic medium but even in free space. This interaction is called the spin-orbit interaction of light. The effects of the spin-orbit interaction of light manifest themselves in a small transverse shift of the beam field longitudinal component from the beam propagation axis in the waist region under the circular polarization sign change. They can be observed both for Gaussian beams and for structured beams. The effects of the spin-orbit interaction of light should be taken into account when nanophotonics devices are created, but the detailed investigation of the effect had not been performed yet due to the low intensity noise image of the beam waist. Precise measurements of the focal waist centerline are needed to determine the transverse shift of the beam field longitudinal component of the asymmetric converging beam’s waist under the circular polarization sign change. We propose methods for determining the transverse and longitudinal positions of the beam waist. Computer image processing methods made it possible to obtain the value of the beam waist's transverse position with an accuracy of 0.1 mm. These methods will allow further testing of the shifts' theoretical predictions, the values of which are the order of 1 mm. The results obtained can also be used for laser processing of materials by polarized light and precise positioning of the beam's focal spot at a surface.
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Статья научная
In this paper, we propose an algorithm for the automatic construction (design) of a computational procedure for non-linear local processing of digital signals/images. The aim of this research is to work out an image processing algorithm with a predetermined computational complexity and achieve the best quality of processing on the existing data set, while avoiding a problem of retraining or doing with less training. To achieve this aim we use a local discrete wavelet transform for a preliminary image analysis and the hierarchical regression to construct a local image processing procedure on the basis of a training dataset. Moreover, we work out a method to decide whether the training process should be completed or continued. This method is based on the functional of full cross-validation control, which allows us to construct the processing procedure with a predetermined computational complexity and veracity, and with the best quality.
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Diamond focusators for far IR lasers
Статья научная
Recently a new technique has been proposed for laser-assisted generation of phase microrelief to manufacture diamond diffractive lenses for the far IR range. In the present paper the realization of diamond diffractive optical elements (DOEs) is considered, able to focus an incoming CO2 laser beam into certain pre-given focal domains. Exemplarily, two completely different DOEs for different tasks of laser beam focusing have been designed by different methods, manufactured and finally investigated by means of optical experiment and computer simulation. Measured intensity distributions in the DOEs' focal planes as well as measured diffraction efficiencies have been compared with related results of computer simulation, and have been found to be in good mutual concordance. Obtained first results indicate that technique of laser-assisted ablation can be effectively used for manufacturing of high quality diamond DOEs for laser beam focusing.
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Diffractive elements for imaging optics of mobile communication devices
Статья научная
An estimate of the permissible width of the working spectral range of optical systems with diffractive elements is given. It takes into account the interval of the angles of incidence of the radiation on the microstructure of the element and it proceeds from the requirement that there is no halo in the image that is visualized by the LCD monitor. It is shown that the design parameters of diffractive elements intended for mobile device cameras are quite achievable for today's technologies of mass production of plastic optics.
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Diffractive optical power of a square diaphragm
Статья научная
The concept of diffractive optical power is extended over the case of a square diaphragm and of the negative Fresnel numbers for the incident wave. The accurate interpolation formula for the image location is represented. It contains the additional factor describing the dependence of the optical power on the incident wave front curvature. The high precision of the approximation is the conclusive evidence for the correctness of the physical model for the focusing action of the diaphragms.
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Document image analysis and recognition: a survey
Статья научная
This paper analyzes the problems of document image recognition and the existing solutions. Document recognition algorithms have been studied for quite a long time, but despite this, currently, the topic is relevant and research continues, as evidenced by a large number of associated publications and reviews. However, most of these works and reviews are devoted to individual recognition tasks. In this review, the entire set of methods, approaches, and algorithms necessary for document recognition is considered. A preliminary systematization allowed us to distinguish groups of methods for extracting information from documents of different types: single-page and multi-page, with text and handwritten contents, with a fixed template and flexible structure, and digitalized via different ways: scanning, photographing, video recording. Here, we consider methods of document recognition and analysis applied to a wide range of tasks: identification and verification of identity, due diligence, machine learning algorithms, questionnaires, and audits. The groups of methods necessary for the recognition of a single page image are examined: the classical computer vision algorithms, i.e., keypoints, local feature descriptors, Fast Hough Transforms, image binarization, and modern neural network models for document boundary detection, document classification, document structure analysis, i.e., text blocks and tables localization, extraction and recognition of the details, post-processing of recognition results. The review provides a description of publicly available experimental data packages for training and testing recognition algorithms. Methods for optimizing the performance of document image analysis and recognition methods are described.
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Статья научная
In this paper, attempts have been made to study the joint effects of apodization and aperture masking on the diffraction images of coherently illuminated straight edge. The Edge-Ringing, Edge-Shift and Edge-Eradient of the edge images have been evaluated for different values of apodization using edge masking of circular apertures. We have considered rotationally symmetric, aberrated coherent optical system. These investigations have lead to the use of certain pupil functions in conjunction with optimal apodizers to assess the quality of edge images. Any obstruction placed in the light path of an optical system prevents waves from a portion of the wavefront in reaching the focal zone. This results in the change in the light flux at every point of the diffraction pattern. This is in turn, depends on the shape and size of the obstruction.
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Efficiency of object identification for binary images
Статья научная
In this paper, a comparative analysis of the correlation-extreme method, the method of contour analysis and the method of stochastic gradient identification in the objects identification for a binary image is carried out. The results are obtained for a situation where possible deformations of an identified object with respect to a pattern can be reduced to a similarity model, that is, the pattern and the object may differ in scale, orientation angle, shift along the base axes, and additive noise. The identification of an object is understood as the recognition of its image with an estimate of the strain parameters relative to the template.
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Erratum: dynamic analysis of optical cell trapping in the ray optics regime
Статья научная
In this additional part of the original paper [1], revised calculations and corrected equations are presented. Also some conclusions from the original paper are revised and discussed briefly.
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Статья
В настоящем дополнении к оригинальной статье [1] исправляется ошибка, допущенная при расчетах спектров отражения и пропускания изогнутого волноводного резонатора Фабри–Перо. Ошибка возникла вследствие пренебрежения оболочечными модами в прямых волноводных участках перед и после исследуемого резонатора (рис. 2а в оригинальной статье). Хотя данные моды не вносят непосредственного вклада в вычисляемую прошедшую и отраженную мощность, их учет необходим для корректного расчета спектров отражения и пропускания резонатора, что было обнаружено после опубликования статьи. В данном дополнении приводятся исправленные результаты, а также некоторые корректировки выводов оригинальной статьи.
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Статья научная
Change detection from synthetic aperture radar images becomes a key technique to detect change area related to some phenomenon as flood and deformation of the earth surface. This paper proposes a transfer learning and Residual Network with 18 layers (ResNet-18) architecture-based method for change detection from two synthetic aperture radar images. Before the application of the proposed technique, batch denoising using convolutional neural network is applied to the two input synthetic aperture radar image for speckle noise reduction. To validate the performance of the proposed method, three known synthetic aperture radar datasets (Ottawa; Mexican and for Taiwan Shimen datasets) are exploited in this paper. The use of these datasets is important because the ground truth is known, and this can be considered as the use of numerical simulation. The detected change image obtained by the proposed method is compared using two image metrics. The first metric is image quality index that measures the similarity ratio between the obtained image and the image of the ground truth, the second metrics is edge preservation index, it measures the performance of the method to preserve edges. Finally, the method is applied to determine the changed area using two Sentinel 1 B synthetic aperture radar images of Eddahbi dam situated in Morocco.
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Статья научная
This paper considers an experimental study of the layout of an active-pulse television measuring system in the problem of assessing the accuracy of measuring the distance to objects using the depth maps. The main technical characteristics and structure of the active-pulse television measuring system layout are described, the description of the multi-zone ranging method used in the experiment is given. The field tests were carried out using a system for terrain orthophotomaps construction by an unmanned aerial vehicle and a geodetic measuring instrument, which is a reference for building a terrain plan and fixing distances between objects on the ground. The technique of carrying out aerial work is described to obtain the necessary data array, on which a digital model and an orthophotomap of the area were subsequently built. Conclusions are drawn about the accuracy of digital terrain models built based on the results of aerial photography from an unmanned aerial vehicle with a geodetic receiver on board and the applicability of these data as reference data for testing a prototype of an active-pulse television measuring system.
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Experimental investigation of multimode dispersionless beams
Статья научная
Laser light modes are beams in whose cross-section the complex amplitude is described by eigenfunctions of the operator of light propagation in the waveguide medium. The fundamental properties of modes are their orthogonality and their ability to retain their structure during propagation for example in a lenslike medium or in free space. Developed diffractive optical elements (DOEs) of MODAN-type open up new promising potentialities of solving the tasks of generation, transformation, superposition of different laser modes and their combinations. Now we present new results obtained by synthesis and investigation of beams consisting of more than one two-dimensional Gaussian laser modes with the same value of propagation constant - multimode dispersionless beams.
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Face anti-spoofing with joint spoofing medium detection and eye blinking analysis
Статья научная
Modern biometric systems based on face recognition demonstrate high recognition quality, but they are vulnerable to face presentation attacks, such as photo or replay attack. Existing face anti-spoofing methods are mostly based on texture analysis and due to lack of training data either use hand-crafted features or fine-tuned pretrained deep models. In this paper we present a novel CNN-based approach for face anti-spoofing, based on joint analysis of the presence of a spoofing medium and eye blinking. For training our classifiers we propose the procedure of synthetic data generation which allows us to train powerful deep models from scratch. Experimental analysis on the challenging datasets (CASIA-FASD, NUUA Imposter) shows that our method can obtain state-of-the-art results.
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Face photo retrieval based on sketches
Статья научная
The paper deals with the problem of the automatic retrieval of face photos using sketch drawings based on the witness description. We propose new methods for the generation of a sketch population from the initial one to improve the performance of sketch-based photo image retrieval systems. The method based on the computation of an average sketch from the generated population has been applied to increase the index of similarity in sketch-photo pairs. It is shown that such sketches are more similar to the original photographic images and their use leads to good results. Results of the experiments on CUHK Face Sketch and CUHK Face Sketch FERET databases and open access databases of photo-sketches pairs are discussed.
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Face recognition based on the proximity measure clustering
Статья научная
In this paper problems of featureless face recognition are considered. The recognition is based on clustering the proximity measures between the distributions of brightness clusters cardinality for segmented images. As a proximity measure three types of distances are used in this work: the Euclidean, cosine and Kullback-Leibler distances. Image segmentation and proximity measure clustering are carried out by means of a software model of the recurrent neural network. Results of the experimental studies of the proposed approach are presented.
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Facedetectnet: face detection via fully-convolutional network
Статья научная
Ace detection is one of the most popular computer vision tasks. There are a lot of face detection approaches proposed including different CNN-based techniques, but the problem of optimal balancing between detection quality and computational speed is still relevant. In this paper we propose new CNN-based solution for face detection called FaceDetectNet. Our CNN architecture is based on ideas of YOLO/DetectNet and GoogleNet architecture supported with some new tools and implementation details created especially for our face detection application. We propose: original iterative proposal clustering (IPC) algorithm for aggregation of output face proposals formed by CNN and the 2-level “weak pyramid” providing better detection quality on the testing sets containing both small and huge images. Our face detection approach is close to previously proposed SSD-based face detection, but the principal difference is that we use the deep features of top hidden CNN layer for forming the face proposals of any size...
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Статья научная
We have studied the nanostructuring and colorizing of the copper surface by scanning with a femtosecond laser beam with a near-Gaussian beam profile. The experimental studies were conducted using a femtosecond laser comprising a Ti:Sapphire oscillator and a multi-pass amplifier with the maximum pulse energy of 0.7 mJ, pulse frequency of 1 kHz, and pulse duration <30 fs. It is shown that the use of a short-pulsed femtosecond laser leads to the formation of wavelength scale periodic surface structures and eventually increases the brightness of the color of the copper surface. It is revealed that via reciprocally scanning the copper surface by multiple ultrashort laser pulses with a weakly asymmetric spatial energy density distribution and an energy density below the material ablation threshold, it is possible to create a combined nanostructure composed of low-spatial-frequency laser-induced periodic surface structures coated with nanoscale roughness. It is shown that relatively minor changes in the nanostructures obtained by scanning the copper surface by multiple ultrashort laser pulses can lead to a significant change in the color during surface colorizing.
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Fine-tuning the hyperparameters of pre-trained models for solving multiclass classification problems
Статья научная
This study is devoted to the application of fine-tuning methods for Transfer Learning models to solve the multiclass image classification problem using the medical X-ray images. To achieve this goal, the structural features of such pre-trained models as VGG-19, ResNet-50, InceptionV3 were studied. For these models, the following fine-tuning methods were used: unfreezing the last convolutional layer and updating its weights, selecting the learning rate and optimizer. As a dataset chest X-Ray images of the Society for Imaging Informatics in Medicine (SIIM), as the leading healthcare organization in its field, in partnership with the Foundation for the Promotion of Health and Biomedical Research of Valencia Region (FISABIO), the Valencian Region Medical ImageBank (BIMCV) ) and the Radiological Society of North America (RSNA) were used. Thus, the results of the experiments carried out illustrated that the pre-trained models with their subsequent tuning are excellent for solving the problem of multiclass classification in the field of medical image processing. It should be noted that ResNet-50 based model showed the best result with 82.74 % accuracy. Results obtained for all models are reflected in the corresponding tables.
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