>> img = imread('airplane.JPG');
>> img = double(img)/255;
>> image(img)
>> imc = img(1:4:end,1:4:end,:);
>> imc = zeros(size(imc));
for i = 1:4, for j = 1:4,
imc = imc + img(i:4:end,j:4:end,:);
end
end
>> imc = imc / 16;
>> seggui(imc)