How can I operate the 2nd part of the following described process of a noisy image of size 256x256 in MATLAB?

1st part: Suppose I have an impulse noisy image and I know the positions of noise in the image. I have placed 0s for noise and 1s for healthy pixels to prepare a noise map.

2nd part: I want to place a 3x3 window over the noisy image having center pixel as noise for each noisy positions detected by the map. I need to find if the number of healthy pixels (N) for every window is greater than 3 or not. If found greater I will find sum of absolute difference (SAD) between healthy pixels and central noisy pixel within that window. This process needs to be repeated for every noisy detected pixel.

Can anyone help me to solve that in MATLAB?

An example is attached herewith.