function [img] = imgExpand(img,levels)
g_filter = [1 4 6 4 1]/16;

for i=1:levels
    img_size = size(img);
    y = zeros(2*img_size);
    y(1:2:2*img_size(1),1:2:2*img_size(2)) = img;
    img = 4*conv2(g_filter,g_filter,y,'same');
end