Gaussian Filter

X = [
    -1,0,1;
    -1,0,1;
    -1,0,1
    ];

Y = [
    -1,-1,-1;
    0,0,0;
    1,1,1;
    ];

si = 0.9;
gaus = (1 / (2 * 3.1416 * si^2)) * exp(-(X.^2 + Y.^2) / (2*si^2));


I = imread('coins.png');
I2 = imnoise(I,'gaussian', 0.02);
I3 = I2;
[row, col] = size(I2);
temp = zeros(3,3);

for i = 1:row-2
    for j = 1:col-2
        N = I2(i:i+2, j:j+2);

           for x = 1:3
               for y = 1:3
                    temp(x,y) = gaus(x,y) * N(x,y);
                end
           end
        t = sum(temp(:));
        I3(i+1, j+1) = t;
    end
end

imshow(I3);