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26th IEEE International Conference on Image Processing (ICIP)

作者： Ghosh, Sanjay Chaudhury, Kunal N. Indian Inst Sci Dept Elect Engn Bengaluru India

ISBN: (纸本)9781538662496

We consider the problem of enhancing images captured under low-light conditions. Several variational and filtering based solutions have been proposed for this problem that are based on the retinex model. The idea in retinex is to first estimate the illumination and reflectance from the observed image, enhance the illumination, and then combine it with the reflectance to get the rectified image. A variant of bilateral filtering, called bright-pass bilateral filtering (BPBF), can be used for illumination estimation. However, BPBF is computation intensive and takes up a significant amount of the processing time. Motivated by recent work, we propose a Fourier approximation of BPBF that can accelerate the filtering (by an order) without loss in visual quality. Experimental results demonstrate that our algorithm is sufficiently fast and can effectively enhance low-light images. In particular, our proposal is competitive with recent algorithms in terms of visual perception and quality metrics.

关键词： low-light enhancement retinex bilateral filter Fourier approximation fast algorithm

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fast ADAPTIVE BILATERAL FILTERING OF COLOR IMAGES 26

FAST ADAPTIVE BILATERAL FILTERING OF COLOR IMAGES

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26th IEEE International Conference on Image Processing (ICIP)

作者： Gavaskar, Ruturaj G. Chaudhury, Kunal N. Indian Inst Sci Dept Elect Engn Bengaluru India

ISBN: (纸本)9781538662496

The bilateral filter is popularly used for image enhancement. By using a range kernel along with a spatial kernel, the filter is able to smooth images without excessive blurring of edges. It has been shown that the enhancement capacity of the filter can be boosted by adapting the width of the range kernel at each pixel. A fast algorithm for grayscale images was recently proposed for this so-called adaptive bilateral filter, which is otherwise computationally expensive. This can trivially be extended for color filtering using channelwise processing. However, developing an efficient algorithm that can exploit correlations between color channels is not straightforward. We show that such a fast algorithm can be developed by first expressing the filtering in terms of the local histogram and then approximating the latter by an uniform distribution. The distribution in question is along the direction of maximum variance in the RGB space, which we compute from the local covariance (this is done efficiently using power iterations). The local covariances in turn are computed using fast convolutions. To demonstrate the effectiveness of our fast algorithm, we apply it for sharpening, detail enhancement, and deblocking.

关键词： color processing bilateral filter fast algorithm histogram covariance

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Overview of fast algorithm in 3D dynamic holographic display

Overview of fast algorithm in 3D dynamic holographic display

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5th International Symposium on Photoelectronic Detection and Imaging (ISPDI) - Optical Storage and Display Technology

作者： Liu, Juan Jia, Jia Pan, Yijie Wang, Yongtian Beijing Inst Technol Sch Opt & Elect Minist Educ China Key Lab Photoelect Imaging Technol & Syst Beijing 100081 Peoples R China

ISBN: (纸本)9780819497826

3D dynamic holographic display is one of the most attractive techniques for achieving real 3D vision with full depth cue without any extra devices. However, huge 3D information and data should be preceded and be computed in real time for generating the hologram in 3D dynamic holographic display, and it is a challenge even for the most advanced computer. Many fast algorithms are proposed for speeding the calculation and reducing the memory usage, such as: look-up table (LUT), compressed look-up table (C-LUT), split look-up table (S-LUT), and novel look-up table (N-LUT) based on the point-based method, and full analytical polygon-based methods, one-step polygon-based methodbased on the polygon-based method. In this presentation, we overview various fast algorithms based on the point-based method and thepolygon-based method, and focus on the fast algorithm (C-LUT) with low memory usage and one-step polygon-based method by the 2D Fourier analysis of the 3D affine transformation. The numerical simulations and the optical experiments are presented, and several other algorithms are compared. The results show that the C-LUT algorithm and the one-step polygon-based method are efficient methods for saving calculation time. It is believed that those methods could be used in the real-time 3D holographic display in the future.

关键词： 3D holographic display Computer generated holograms fast algorithm

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Amixed-type Galerkin variational formulation and fast algorithms for variable-coefficient fractional diffusion equations

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MATHEMATICAL METHODS IN THE APPLIED SCIENCES 2017年第14期40卷 5018-5034页

作者： Li, Yongshan Chen, Huanzhen Wang, Hong Shandong Normal Univ Coll Math Sci Jinan 250014 Shandong Peoples R China Univ South Carolina Dept Math Columbia SC 29208 USA

We consider the variable-coefficient fractional diffusion equations with two-sided fractional derivative. By introducing an intermediate variable, we propose amixed-type Galerkin variational formulation and prove the existence and uniqueness of the variational solution over H-0(1) (Omega) X H1-beta/2 (Omega). On the basis of the formulation, we develop a mixed-type finite element procedure on commonly used finite element spaces and derive the solvability of the finite element solution and the error bounds for the unknown and the intermediate variable. For the Toeplitz-like linear system generated by discretization, we design a fast conjugate gradient normal residual method to reduce the storage from O(N-2)/ to O(N-2) and the computing cost from O(N-3) to O(N log N). Numerical experiments are included to verify our theoretical findings. Copyright (C) 2017 John Wiley & Sons, Ltd.

关键词： mixed-type Galerkin variational formulation fractional diffusion equation finite element solvability error bounds fast algorithm

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A Priori Error Analysis for Time-Stepping Discontinuous Galerkin Finite Element Approximation of Time Fractional Optimal Control Problem

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JOURNAL OF SCIENTIFIC COMPUTING 2019年第2期80卷 993-1018页

作者： Zhang, Chenyang Liu, Huipo Zhou, Zhaojie Shandong Normal Univ Sch Math & Stat Jinan Shandong Peoples R China Inst Appl Phys & Computat Math Beijing Peoples R China

In this paper a priori error analysis for time-stepping discontinuous Galerkin finite element approximation of optimal control problem governed by time fractional diffusion equation is presented. A time-stepping discontinuous Galerkin finite element method and variational discretization approach are used to approximate the state and control variables respectively. Regularity of the optimal control problem is discussed. Since the time fractional derivative is nonlocal, in order to reduce the computational cost a fast gradient projection algorithm is designed for the control problem based on the block triangular Toeplitz structure of the discretized state equation and adjoint state equation. Numerical examples are carried out to illustrate the theoretical findings and fast algorithm.

关键词： Time-stepping discontinuous Galerkin method Time fractional diffusion equation Optimal control problem A priori error estimate fast algorithm 49J20 49K20 65N15 65N30

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Accelerated Computation of the Physical Optics Approximation for Near-Field Single- and Double-Bounces Backscattering

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2019年第12期67卷 7518-7527页

作者： Bourlier, Christophe Kubicke, Gildas Pouliguen, Philippe Univ Nantes CNRS IETR UMR 6164 F-44000 Nantes France DGA DT MI F-35998 Rennes France DGA AID F-75509 Paris France

This article deals with the acceleration of the physical optics (PO) approximation for the backscattering computation in the near and far fields, for both single-bounce (SB) and double-bounce (DB) PO contributions. It is based on physical arguments, which allow us to apply either a closed-form expression (rapid calculation) or a numerical double integration to evaluate the scattered field from subsurfaces of a given mesh. The use of the closed-form expression is governed by two criteria, which must be extended to the bistatic case and also to the DB: the conventional Fraunhofer (related to the far-field zone) criterion and the chord error (related to the surface curvature) criterion. The proposed method is tested on a dihedral geometry.

关键词： Geometry Physical optics Optical surface waves Scattering Surface waves Antennas Surface impedance fast algorithm high-frequency methods physical optics (PO) radar cross section (RCS)

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The Temporal Second Order Difference Schemes Based on the Interpolation Approximation for the Time Multi-term Fractional Wave Equation

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JOURNAL OF SCIENTIFIC COMPUTING 2019年第1期78卷 467-498页

作者： Sun, Hong Zhao, Xuan Sun, Zhi-zhong Nanjing Inst Technol Dept Math & Phys Nanjing 211167 Jiangsu Peoples R China Southeast Univ Jiangsu Prov Key Lab Networked Collect Intelligen Sch Math Nanjing 210096 Jiangsu Peoples R China Southeast Univ Sch Math Nanjing 210096 Jiangsu Peoples R China

In this paper, two temporal second-order schemes are derived and analyzed for the time multi-term fractional diffusion-wave equation based on the order reduction technique. The weighted average at two time levels is applied to the discretization of the spatial derivative, in which the weight coefficient corresponds to the optimal point for the time discretization. The two difference schemes are proved to be uniquely solvable. The stability and convergence are rigorously investigated utilizing the energy method. In addition, a fast difference scheme is also presented. The applicability and the accuracy of the schemes are demonstrated by several numerical experiments.

关键词： Fractional diffusion-wave equation Multi-term fractional derivatives Difference scheme Stability Convergence fast algorithm

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Multiplicative Noise Removal Based on the Smooth Diffusion Equation

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JOURNAL OF MATHEMATICAL IMAGING AND VISION 2019年第6期61卷 763-779页

作者： Shan, Xiujie Sun, Jiebao Guo, Zhichang Harbin Inst Technol Dept Math Harbin 150001 Heilongjiang Peoples R China

The multiplicative noise removal problem is of momentous significance in various image processing applications. In this paper, a nonlinear diffusion equation with smooth solution is proposed to remove multiplicative Gamma noise. The diffusion coefficient takes full advantage of two features of multiplicative noise image, namely, gradient information and gray level information, which makes the model has the ability to remove high level noise effectively and protect the edges. The existence of the solution has been analyzed by Schauder's fixed-point theorem. Some other theoretical properties such as the maximum principle are also presented in the paper. In the numerical aspect, the explicit finite difference method, fast explicit diffusion method, additive operator splitting method and Krylov subspace spectral method are employed to implement the proposed model. Experimental results show that the fast explicit diffusion method achieves a better trade-off between computational time and denoising performance, and the Krylov subspace spectral method gets better restored results in the visual aspect. In addition, the capability of the proposed model for denoising is illustrated by comparison with other denoising models.

关键词： Multiplicative noise removal Diffusion equation Smooth solution fast algorithm

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Early termination strategy of HEVC based on statistical models

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The Journal of China Universities of Posts and Telecommunications 2019年第5期26卷 72-81页

作者： Liu Yitong Tian Wang Li Yuchen Yang Hongwen School of Information and Communication Engineering Beijing University of Posts and Telecommunications

High efficiency video coding(HEVC)uses half of the bitrate compared to H.264/advanced video coding(AVC)for encoding the same sequence with similar *** of the advanced hierarchical structures of coding units(CUs),predicting units(PUs),and transform units(TUs),HEVC can better adapt when encoding full high definition(HD)and ultra high definition(UHD)*** the expense of encoding efficiency,the complexity of HEVC sharply increases compared to H.264/AVC,mainly due to its quad-tree structure that splits *** this study,the probability distribution,which is generated by a rate distortion optimizing(RDO)cost,is ***,an early terminating method is proposed to decrease the complexity of the HEVC based on probability *** experiment shows that the coding time is reduced by 44.9%for HEVC intra coding,at the cost of a 0.61%increase in the Bj?ntegaard delta rate(BD-rate),on average.

关键词： HEVC early termination statistical model fast algorithm

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Finite Element Approximation of Optimal Control Problem Governed by Space Fractional Equation

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JOURNAL OF SCIENTIFIC COMPUTING 2019年第3期78卷 1840-1861页

作者： Zhou, Zhaojie Tan, Zhiyu Shandong Normal Univ Sch Math & Stat Jinan Shandong Peoples R China Hong Kong Baptist Univ Dept Math Kowloon Tong Hong Kong Peoples R China

In this paper we investigate finite element approximation of optimal control problem governed by space fractional diffusion equation with control constraints. The control variable is approximated by piecewise constant. Regularity estimate for the control problem is proved based on the first order optimality system and a priori error estimates for the state, the adjoint state and the control variables are derived. Due to the nonlocal property of fractional derivative, which will leads to a full stiff matrix, we develop a fast primal dual active set algorithm for the control problem. Numerical examples are given to illustrate the theoretical findings and the efficiency of the fast algorithm.

关键词： Finite element method Optimal control problem Space fractional equation Primal dual active set algorithm fast algorithm

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