423 research outputs found
Recent Progress in Image Deblurring
This paper comprehensively reviews the recent development of image
deblurring, including non-blind/blind, spatially invariant/variant deblurring
techniques. Indeed, these techniques share the same objective of inferring a
latent sharp image from one or several corresponding blurry images, while the
blind deblurring techniques are also required to derive an accurate blur
kernel. Considering the critical role of image restoration in modern imaging
systems to provide high-quality images under complex environments such as
motion, undesirable lighting conditions, and imperfect system components, image
deblurring has attracted growing attention in recent years. From the viewpoint
of how to handle the ill-posedness which is a crucial issue in deblurring
tasks, existing methods can be grouped into five categories: Bayesian inference
framework, variational methods, sparse representation-based methods,
homography-based modeling, and region-based methods. In spite of achieving a
certain level of development, image deblurring, especially the blind case, is
limited in its success by complex application conditions which make the blur
kernel hard to obtain and be spatially variant. We provide a holistic
understanding and deep insight into image deblurring in this review. An
analysis of the empirical evidence for representative methods, practical
issues, as well as a discussion of promising future directions are also
presented.Comment: 53 pages, 17 figure
Brief Analysis on the Artistic Technique of Blurring Narrative Subject and its Extension —Take Yu Dafu’s “Degradation” as an Example
As a representative work of vernacular novels in Chinese new literature, “Degradation” sets up an unnamed protagonist and focuses on his inner world for a deep and comprehensive portrayal, thus forming the main content of the novel. This paper will explore the reason why the protagonist of the novel unnamed and the design idea behind it, discuss the revolutionary significance of this method of vague narrative by contrasting with previous literature, and its extension in other art forms today
Intense keV isolated attosecond pulse generation by orthogonally polarized multicycle midinfrared two-color laser field
We theoretically investigate the generation of intense keV attosecond pulses
in an orthogonally polarized multicycle midinfrared two-color laser field. It
is demonstrated that multiple continuum-like humps, which have a spectral width
of about twenty orders of harmonics and an intensity of about one order higher
than adjacent normal harmonic peaks, are generated under proper two-color
delays, owing to the reduction of the number of electron-ion recollisions and
suppression of inter-half-cycle interference effect of multiple electron
trajectories when the long wavelength midinfrared driving field is used. Using
the semiclassical trajectory model, we have revealed the two-dimensional
manipulation of the electron-ion recollision process, which agrees well with
the time frequency analysis. By filtering these humps, intense isolated
attosecond pulses are directly generated without any phase compensation. Our
proposal provides a simple technique to generate intense isolated attosecond
pulses with various central photon energies covering the multi-keV spectral
regime by using multicycle driving pulses with high pump energy in experiment.Comment: 11 pages,5 figures, research articl
Richardson Extrapolation-Based High Accuracy High Efficiency Computation for Partial Differential Equations
In this dissertation, Richardson extrapolation and other computational techniques are used to develop a series of high accuracy high efficiency solution techniques for solving partial differential equations (PDEs).
A Richardson extrapolation-based sixth-order method with multiple coarse grid (MCG) updating strategy is developed for 2D and 3D steady-state equations on uniform grids. Richardson extrapolation is applied to explicitly obtain a sixth-order solution on the coarse grid from two fourth-order solutions with different related scale grids. The MCG updating strategy directly computes a sixth-order solution on the fine grid by using various combinations of multiple coarse grids. A multiscale multigrid (MSMG) method is used to solve the linear systems resulting from fourth-order compact (FOC) discretizations. Numerical investigations show that the proposed methods compute high accuracy solutions and have better computational efficiency and scalability than the existing Richardson extrapolation-based sixth order method with iterative operator based interpolation.
Completed Richardson extrapolation is explored to compute sixth-order solutions on the entire fine grid. The correction between the fourth-order solution and the extrapolated sixth-order solution rather than the extrapolated sixth-order solution is involved in the interpolation process to compute sixth-order solutions for all fine grid points. The completed Richardson extrapolation does not involve significant computational cost, thus it can reach high accuracy and high efficiency goals at the same time.
There are three different techniques worked with Richardson extrapolation for computing fine grid sixth-order solutions, which are the iterative operator based interpolation, the MCG updating strategy and the completed Richardson extrapolation. In order to compare the accuracy of these Richardson extrapolation-based sixth-order methods, truncation error analysis is conducted on solving a 2D Poisson equation. Numerical comparisons are also carried out to verify the theoretical analysis.
Richardson extrapolation-based high accuracy high efficiency computation is extended to solve unsteady-state equations. A higher-order alternating direction implicit (ADI) method with completed Richardson extrapolation is developed for solving unsteady 2D convection-diffusion equations. The completed Richardson extrapolation is used to improve the accuracy of the solution obtained from a high-order ADI method in spatial and temporal domains simultaneously. Stability analysis is given to show the effects of Richardson extrapolation on stable numerical solutions from the underlying ADI method
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