function bernsen(img, ramka)
    img = rgb2gray(img);
    [h w] = size(img);
    img = double(img);
    sz = (ramka - 1)/2;

    out = zeros(h, w);

    for i = (1 + sz):(h - sz)
        for j = (1 + sz):(w - sz)
            A = img(i-sz:i+sz,j-sz:j+sz);
            a = min(A)
            b = max(A);
            sr = (a+b)/2;
            if(img(i,j)>sr) then
                out(i,j) = 255
            end
        end
    end

    out = uint8(out)
    imshow(out);
endfunction

I = imread('lena.jpg')
bernsen(I, 3);