        bw = zeros(200,200); bw(50,50) = 1; bw(50,150) = 1;
        bw(150,100) = 1;
        D1 = bwdist(bw,'euclidean');
        D2 = bwdist(bw,'cityblock');
        D3 = bwdist(bw,'chessboard');
        D4 = bwdist(bw,'quasi-euclidean');
        figure
        subplot(2,2,1), subimage(mat2gray(D1)), title('Euclidean')
        hold on, imcontour(D1)
        subplot(2,2,2), subimage(mat2gray(D2)), title('City block')
        hold on, imcontour(D2)
        subplot(2,2,3), subimage(mat2gray(D3)), title('Chessboard')
        hold on, imcontour(D3)
        subplot(2,2,4), subimage(mat2gray(D4)), title('Quasi-Euclidean')
        hold on, imcontour(D4)