Smoothing Nonlinear Conjugate Gradient Method for Image Restoration Using Nonsmooth Nonconvex Minimization

Xiaojun Chen, Weijun Zhou
2010 SIAM Journal of Imaging Sciences  
Image restoration problems are often converted into large-scale, nonsmooth and nonconvex optimization problems. Most existing minimization methods are not efficient for solving such problems. It is well-known that nonlinear conjugate gradient methods are preferred to solve large-scale smooth optimization problems due to their simplicity, low storage, practical computation efficiency and nice convergence properties. In this paper, we propose a smoothing nonlinear conjugate gradient method where
more » ... n intelligent scheme is used to update the smoothing parameter at each iteration and guarantees that any accumulation point of a sequence generated by this method is a Clarke stationary point of the nonsmooth and nonconvex optimization problem. Moreover, we present a class of smoothing functions and show their approximation properties. This method is easy to implement without adding any new variables. Three image restoration problems with different pixels and different regularization terms are used in numerical tests. Experimental results and comparison with the continuation method in [M.Nikolova et al, SIAM J. Imaging Sciences, 1(2008), pp.2-25] show the efficiency of the proposed method.
doi:10.1137/080740167 fatcat:xgtearfmyvbt3i22ajw3ahcp3i