clc, clearvars, close all

I = imread('cameraman.tif');
IF = I;

[row col] = size(I);

for i = 2:row-1
    for j = 2:col-1
        Mask = I(i-1:i+1, j-1:j+1);
        Mean_mask = mean(mean(Mask));
        IF(i,j) = Mean_mask;
    end
end

figure, imshow(IF), title('Mean--Filtered--Image')