$4.$ The mean filter is a basic convolutional operation in image processing. A small convolution mask $(3$x$3,$ perhaps $5$x$5)$ with uniform weights in all cells summing to $1$ is passed over the image; this replaces each pixel with the mean value of the pixels in its immediate neighborhood. The resulting image is a bit blurrier, but a lot of noise $($especially salt$-$and$-$pepper or Gaussian noise$)$ is removed.

We are going to implement the mean filter in a neurocomputer. The convolution mask to be applied to an image is: