Edinburgh Napier University

About: Edinburgh Napier University is a education organization based out in Edinburgh, United Kingdom. It is known for research contribution in the topics: Population & Health care. The organization has 2665 authors who have published 6859 publications receiving 175272 citations.

Enhancement of Underwater Images With Statistical Model of Background Light and Optimization of Transmission Map

Abstract: Underwater images often have severe quality degradation and distortion due to light absorption and scattering in the water medium. A hazy image formation model is widely used to restore the image quality. It depends on two optical parameters: the background light (BL) and the transmission map (TM). Underwater images can also be enhanced by color and contrast correction from the perspective of image processing. In this paper, we propose an effective underwater image enhancement method for underwater images in composition of underwater image restoration and color correction. Firstly, a manually annotated background lights (MABLs) database is developed. With reference to the relationship between MABLs and the histogram distributions of various underwater images, robust statistical models of BLs estimation are provided. Next, the TM of R channel is roughly estimated based on the new underwater dark channel prior (NUDCP) via the statistic of clear and high resolution (HD) underwater images, then a scene depth map based on the underwater light attenuation prior (ULAP) and an adjusted reversed saturation map (ARSM) are applied to compensate and modify the coarse TM of R channel. Next, TMs of G-B channels are estimated based on the difference of attenuation ratios between R and G-B channels. Finally, to improve the color and contrast of the restored image with a dehazed and natural appearance, a variation of white balance is introduced as post-processing. In order to guide the priority of underwater image enhancement, sufficient evaluations are conducted to discuss the impacts of the key parameters including BL and TM, and the importance of the color correction. Comparisons with other state-of-the-art methods demonstrate that our proposed underwater image enhancement method can achieve higher accuracy of estimated BLs, lower computation time, overall superior performance, and better information retention.

Two Years of Nonthermal Emission from the Binary Neutron Star Merger GW170817: Rapid Fading of the Jet Afterglow and First Constraints on the Kilonova Fastest Ejecta

Abstract: We present Chandra and VLA observations of GW170817 at ~521-743 days post merger, and a homogeneous analysis of the entire Chandra data set. We find that the late-time non-thermal emission follows the expected evolution from an off-axis relativistic jet, with a steep temporal decay $F_{\ u}\\propto t^{-1.95\\pm0.15}$ and a simple power-law spectrum $F_{\ u}\\propto \ u^{-0.575\\pm0.007}$. We present a new method to constrain the merger environment density based on diffuse X-ray emission from hot plasma in the host galaxy and we find $n\\le 9.6 \\times 10^{-3}\\,\\rm{cm^{-3}}$. This measurement is independent from inferences based on the jet afterglow modeling and allows us to partially solve for model degeneracies. The updated best-fitting model parameters with this density constraint are a fireball kinetic energy $E_0 = 1.5_{-1.1}^{+3.6}\\times 10^{49}\\,\\rm{erg}$ ($E_{iso}= 2.1_{-1.5}^{+6.4}\\times10^{52}\\, \\rm{erg}$), jet opening angle $\\theta_{0}= 5.9^{+1.0}_{-0.7}\\,\\rm{deg}$ with characteristic Lorentz factor $\\Gamma_j = 163_{-43}^{+23}$, expanding in a low-density medium with $n_0 = 2.5_{-1.9}^{+4.1} \\times 10^{-3}\\, \\rm{cm^{-3}}$ and viewed $\\theta_{obs} = 30.4^{+4.0}_{-3.4}\\, \\rm{deg}$ off-axis. The synchrotron emission originates from a power-law distribution of electrons with $p=2.15^{+0.01}_{-0.02}$. The shock microphysics parameters are constrained to $\\epsilon_{\\rm{e}} = 0.18_{-0.13}^{+0.30}$ and $\\epsilon_{\\rm{B}}=2.3_{-2.2}^{+16.0} \\times 10^{-3}$. We investigate the presence of X-ray flares and find no statistically significant evidence of $\\ge2.5\\sigma$ of temporal variability at any time. Finally, we use our observations to constrain the properties of synchrotron emission from the deceleration of the fastest kilonova ejecta with energy $E_k^{KN}\\propto (\\Gamma\\beta)^{-\\alpha}$ into the environment, finding that shallow stratification indexes $\\alpha\\le6$ are disfavored.

An Experimental-Based Review of Image Enhancement and Image Restoration Methods for Underwater Imaging

Abstract: Underwater images play a key role in ocean exploration but often suffer from severe quality degradation due to light absorption and scattering in water medium. Although major breakthroughs have been made recently in the general area of image enhancement and restoration, the applicability of new methods for improving the quality of underwater images has not specifically been captured. In this paper, we review the image enhancement and restoration methods that tackle typical underwater image impairments, including some extreme degradations and distortions. First, we introduce the key causes of quality reduction in underwater images, in terms of the underwater image formation model (IFM). Then, we review underwater restoration methods, considering both the IFM-free and the IFM-based approaches. Next, we present an experimental-based comparative evaluation of the state-of-the-art IFM-free and IFM-based methods, considering also the prior-based parameter estimation algorithms of the IFM-based methods, using both subjective and objective analyses (the used code is freely available at https://github.com/wangyanckxx/Single-Underwater-Image-Enhancement-and-Color-Restoration). Starting from this paper, we pinpoint the key shortcomings of existing methods, drawing recommendations for future research in this area. Our review of underwater image enhancement and restoration provides researchers with the necessary background to appreciate challenges and opportunities in this important field.

Changing reasons for public private partnerships.

Abstract: This article considers the micro- and macro-economic benefits and costs of PPPs and some implications of implementing new international accounting standards. If public sector financial costs are forced to move ‘on balance sheet’, then there are likely to be impacts on the use in PPPs by governments and other public bodies. This may move the basis of PPP choice towards a more level playing-field with other financing sources, potentially give a more realistic measure of future public commitments and liabilities and reduce incentives to use PPPs for budget enlargement. There may be a refocusing upon the potential efficiency gains of PPPs and a reduction in their use, in some cases.