To date, much progress has been achieved on daytime image dehazing, yet the nighttime dehazing problem is still not well addressed. Different from the imaging conditions in the daytime, the ambient illumination in the nighttime hazy scene is usually not globally isotropic due to the non-uniform incident lights from multiple artificial light sources. Currently, almost all the existing nighttime dehazing methods use a certain kind of image priors, whereby these spatial filtering based priors are not widely applicable in nighttime hazy scenes. For example, the maximum reflectance prior (MRP) cannot handle the dark regions well and the dark channel prior (DCP) is not valid in the light source regions. In this paper, we propose an efficient and fast method for nighttime image dehazing. By exploring the visual properties of hazy images, we construct an effective linear model to build the connection between the transmission and multiple haze-relevant features. Towards solving this model, a data-driven approach is adopted to learn the unknown coefficients. Operating on the pixel level, this novel approach requires no further refinement of transmission map as used in those prior-based methods. In addition, aiming at solving the problem of halo effect around the light sources caused by MRP, we introduce a color-dependant MRP method for color correction. We demonstrate the effectiveness of our method on a number of experiments compared to the state-of-the-art nighttime dehazing methods.

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.Laser-induced damage threshold (LIDT) is investigated at several wavelengths in the high-purity silica optical fiber. The finite element method (FEM) is used to study transmission mode, LIDT, temperature distribution, and thermal stress distribution of the fiber. Our results show that the center of the front surface is subjected to severe thermal effects under laser irradiation and consequently, and it is susceptible damage. The variations in temperature and thermal stress are identified as increasing with laser fluences, which show a similar tendency. When laser fluences surpass the LIDT, such as 35  GW  /  cm2, the temperature at the front surface center shows a sudden growth and the melting damage appears, and no stress damage occurs at this time. Notably, the melting effect of high purity fused silica optical fiber is simulated by numerical calculation based on ray optics for the first time. Our research can provide systematic FEM simulations for the LIDT of silica optical fibers.