1. INTRODUCTION
Image denoising is a fundamental problem in the field of image processing and computer vision. Numerous image denoising algorithms exist in the computer vision and image processing literatures. The nonlinear diffusion approach was first proposed by Perona and Malik [1]. Later their original model was improved by Catt!e et al [2] from both theoretical and practical viewpoints. An anisotropic extension with a diffusion tensor was presented by Weickert [3] to improve the processing quality. Nonlinear anisotropic diffusion has been proposed and applied to various fields in image processing in recent years,