在基于Retinex分解的低照度图像增强算法中,通过同时估计反射层和亮度层进行反射层恢复是一种流行且有效的方法,但算法结构较为复杂,实现难度大。这是因为恢复反射率是一个约束优化问题,不能用简单的优化技术来解决。本文提出了一种细...在基于Retinex分解的低照度图像增强算法中,通过同时估计反射层和亮度层进行反射层恢复是一种流行且有效的方法,但算法结构较为复杂,实现难度大。这是因为恢复反射率是一个约束优化问题,不能用简单的优化技术来解决。本文提出了一种细节显著性估计方法,可以利用简单的梯度下降优化技术从图像中恢复出反射层。该方法是基于我们所提出假设——暗区域近似(dark region approximation,DRA):由于低照度图像暗区域中的光照很弱,因此将其忽略不计,即将输入图像中暗区域的灰度分布直接近似为反射层。首先利用高斯场准则构建目标函数,通过基于DRA的Retinex模型估计细节显著层;然后用拟牛顿法求解该无约束优化问题;最后,从细节显著层中恢复出反射层作为最终增强结果。实验结果表明,与现有同类方法相比,我们的方法在增强效果和计算效率方面都具有优势。展开更多
Part II of this study detects the dominant decadal-centennial timescales in four SST indices up to the 2010/2011 winter and tries to relate them to the observed 11-yr and 88-yr solar activity with the sunspot number u...Part II of this study detects the dominant decadal-centennial timescales in four SST indices up to the 2010/2011 winter and tries to relate them to the observed 11-yr and 88-yr solar activity with the sunspot number up to Solar Cycle 24. To explore plausible solar origins of the observed decadal-centennial timescales in the SSTs and climate variability in general, we design a simple one-dimensional dynamical system forced by an annual cycle modulated by a small-amplitude single- or multi-scale ＂solar activity.＂ Results suggest that nonlinear harmonic and subharmonic resonance of the system to the forcing and period-doubling bifurcations are responsible for the dominant timescales in the system, including the 60-yr timescale that dominates the Atlantic Multidecadal Oscillation. The dominant timescales in the forced system depend on the system＇s parameter setting. Scale enhancement among the dominant response timescales may result in dramatic amplifications over a few decades and extreme values of the time series on various timescales. Three possible energy sources for such amplifications and extremes are proposed. Dynamical model results suggest that solar activity may play an important yet not well recognized role in the observed decadal-centennial climate variability. The atmospheric dynamical amplifying mechanism shown in Part I and the nonlinear resonant and bifurcation mechanisms shown in Part II help us to understand the solar source of the multi-scale climate change in the 20th century and the fact that different solar influenced dominant timescales for recurrent climate extremes for a given region or a parameter setting. Part II also indicates that solar influences on climate cannot be linearly compared with non-cyclic or sporadic thermal forcings because they cannot exert their influences on climate in the same way as the sun does.展开更多
文摘在基于Retinex分解的低照度图像增强算法中,通过同时估计反射层和亮度层进行反射层恢复是一种流行且有效的方法,但算法结构较为复杂,实现难度大。这是因为恢复反射率是一个约束优化问题,不能用简单的优化技术来解决。本文提出了一种细节显著性估计方法,可以利用简单的梯度下降优化技术从图像中恢复出反射层。该方法是基于我们所提出假设——暗区域近似(dark region approximation,DRA):由于低照度图像暗区域中的光照很弱,因此将其忽略不计,即将输入图像中暗区域的灰度分布直接近似为反射层。首先利用高斯场准则构建目标函数,通过基于DRA的Retinex模型估计细节显著层;然后用拟牛顿法求解该无约束优化问题;最后,从细节显著层中恢复出反射层作为最终增强结果。实验结果表明,与现有同类方法相比,我们的方法在增强效果和计算效率方面都具有优势。
基金provided by the LASG State Key Laboratory Special Fund for this research project
文摘Part II of this study detects the dominant decadal-centennial timescales in four SST indices up to the 2010/2011 winter and tries to relate them to the observed 11-yr and 88-yr solar activity with the sunspot number up to Solar Cycle 24. To explore plausible solar origins of the observed decadal-centennial timescales in the SSTs and climate variability in general, we design a simple one-dimensional dynamical system forced by an annual cycle modulated by a small-amplitude single- or multi-scale ＂solar activity.＂ Results suggest that nonlinear harmonic and subharmonic resonance of the system to the forcing and period-doubling bifurcations are responsible for the dominant timescales in the system, including the 60-yr timescale that dominates the Atlantic Multidecadal Oscillation. The dominant timescales in the forced system depend on the system＇s parameter setting. Scale enhancement among the dominant response timescales may result in dramatic amplifications over a few decades and extreme values of the time series on various timescales. Three possible energy sources for such amplifications and extremes are proposed. Dynamical model results suggest that solar activity may play an important yet not well recognized role in the observed decadal-centennial climate variability. The atmospheric dynamical amplifying mechanism shown in Part I and the nonlinear resonant and bifurcation mechanisms shown in Part II help us to understand the solar source of the multi-scale climate change in the 20th century and the fact that different solar influenced dominant timescales for recurrent climate extremes for a given region or a parameter setting. Part II also indicates that solar influences on climate cannot be linearly compared with non-cyclic or sporadic thermal forcings because they cannot exert their influences on climate in the same way as the sun does.
