Document Type : Research Article
Faculty of Engineering, mohaghegh ardabili University of Technology, ardabill, Iran.
Faculty of Electrical and Computer Engineering, Babol Noshirvani University of Technology,Babol, Iran
Faculty of Engineering, Mohaghegh Ardabili University, Ardabil, Iran
Learning and reconstruction_based methods are two main approaches to solve single image super resolution (SISR) problem. In this paper, to exploit the advantages of both the learning based and reconstruction based approaches, we propose a new SISR framework by combining them which can effectively utilize their benefits. the external directional dictionaries (EDD) are learned from external high quality images. Also, we embed the nonlocal means (NLM) filter and an isotropic total variation (TV) scheme in the reconstruction based method. We suggest a new supervised clustering scheme via curvelet based direction extraction method (CCDE) to learn the external directional dictionaries from candidate patches with sharp edges. Each input patch is coded by all EDD. Each of the reconstructed patches under different EDD is applied with a weighted penalty to characterize the given input patch. To disclose new details, the local smoothness and nonlocal self_similarity priors are added on the recovered patch by TV scheme and NLM filter, respectively. Extensive experimental results validate the effectiveness and robustness of the proposed method comparing with the state-of- the-art algorithms in SISR methods. Our proposed schemes can retrieve more fine structures and obtain superior results than the competing methods with the scaling factors of 2 and 3.