Smoothing nonlinear conjugate gradient method for image restoration using nonsmooth nonconvex minimization

Xiaojun Chen, Weijun Zhou

Research output: Journal article publicationJournal articleAcademic researchpeer-review

107 Citations (Scopus)


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 an 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 show the efficiency of the proposed method.
Original languageEnglish
Pages (from-to)765-790
Number of pages26
JournalSIAM Journal on Imaging Sciences
Issue number4
Publication statusPublished - 3 Dec 2010


  • Image restoration
  • Nonlinear conjugate gradient method
  • Nonsmooth and nonconvex optimization
  • Potential function
  • Regularization
  • Smooth approximation

ASJC Scopus subject areas

  • General Mathematics
  • Applied Mathematics


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