Sequentially combined mean-median filter for high density salt and pepper noise removal

Salt and pepper noise removal is extremely challenging task when the noise density is very high in the corrupted image. Usually the existing filters are not capable of removing this noise above 70% density. This paper proposes a Sequentially Combined Mean-Median Filter (SCMMF) based on combination of arithmetic mean and median technique. A binary flag image is generated with the help of identified noisy pixels which are first replaced by a value calculated by plus (+) operation with nearest pixels intensities. The remaining noisy pixels are then replaced by neighbourhood mean operations. Finally the image quality is enhanced by the median of the corresponding window. Border operation is also incorporated to preserve the image size. Experimental results show that SCMMF is outstanding from visual qualitative judgments for a number of standard images. Moreover, this combined filter outperform over the existing with respect to MSE, PSNR, and SSIM comparison even at 92% noise density level.