An automatic stopping criterion for nonlinear anisotropic diffusion

Nonlinear anisotropic diffusion (NAD) filtering is a procedure based on nonlinear evolution PDEs which seeks to improve images qualitatively by removing noise while preserving details and even enhancing edges. However, well-known implementations are sensitive to parameters which are necessarily tuned to sharpen a narrow range of edge slopes; otherwise, edges are either blurred or staircased [Kee2002]. One important parameter is the iterations number, for that reason, in this paper a stopping criterion to halt the diffusion process is proposed. To meet this goal, two stopping criteria were compared. The first is the stopping criterion proposed by Joao et. al. [Joã2016], which is based on the Mean Squared Error (MSE). The second is our proposed method based on the CIRR contrast measure. To this end, a comparative analysis of five diffusion methods is performed. Four of them are nonlinear anisotropic diffusion methods and the fifth is the Perona-Malik method. According to the tests performed, the number of iterations required by the smoothing algorithms using the proposed stopping criterion is lower.