Average filter is one of the most commonly used linear low-pass smoothing filters, which can suppress the additive noise in the image, but at the same time it will blur the image. Median filter is one of the most commonly used nonlinear smoothing filters, which can eliminate isolated noise points in the image and produce less blur. Generally speaking, the effect of median filtering is better than the low-pass filtering of neighborhood average processing, and its main feature is that the outline in the filtered image is clearer. Therefore, median filtering is used to filter out the salt and pepper noise in the image.