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 x 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 MEstimator. 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.