Impulsive noise filtering using a Median Redescending M-Estimator

Salt and Pepper noise removal is an important image preprocessing task, it has two simultaneous demands: the suppression of impulses and the preservation of edges. To address this problem in gray scale images, we propose an efficient method which consists of introducing a Redescending M-Estimator within of the Median-Estimator scheme. The Redescending M-Estimator controls the magnitude of the Salt or Pepper impulses and deletes them when it is necessary; the remaining pixels in the neighborhood are processed by the Median-Estimator in order to obtain an estimation of a noise free pixel. The proposed scheme is applied on the entire image using sliding windows of size 5 × 5; the local information obtained by this window is used to calculate the thresholds and the parameters that characterize the influence functions tested in the Redescending M-Estimator. To improve the suppression ability of our proposal a pulse detector is used, it identifies when is necessary to submit each pixel to the denoising process. The effectiveness of our proposal is verified by quantitative and qualitative results.