function testgD
f = im2double(imread('cameraman.tif'));

sigma = 1;
xorder = 1;
yorder = 1;

g = gD(f, sigma, 1, 0);
h = gD(f, sigma, 1, 1);
i = gD(f, sigma, 2, 0);
j = gD(f, sigma, 2, 2);

%subplot(2,2,1), imshow(g,[]);
%subplot(2,2,3), imshow(i,[]);

subplot(1,2,1), imshow(h,[]);
subplot(1,2,2), imshow(j,[]);

%subplot(1,2,1), imshow(1-normalize(h));
%subplot(1,2,2), imshow(1-normalize(j));

%subplot(2,2,3), plot(gDx);
%subplot(2,2,4), plot(gDy);