Switching median and morphological filter for impulse noise removal from digital images

A switching median and morphological filter is presented for removing impulse noise. In the proposed filter, the noise detector is first adopted to identify noise pixels by combining the morphological gradient based on the erosion and dilation operators with the top-hat transform. Then the detected impulses are removed by the hybrid filter, which combines the improved median filter using only the noise-free pixels with the conditional morphological filter using the improved morphological operations. Extensive simulations demonstrate that the proposed filter can realize accurate noise detection and it has significantly better restoration performance than a number of decision-based filters at the various noise ratios.