def make_2d_kernels():
    # for the peripheral elements
    pkb = np.zeros((3,3))
    pkb[1,1] = 1
    pkb[0,1] = -1

    # for the diagonal elements
    dkb = np.zeros((3,3))
    dkb[1,1] = 1
    dkb[0,0] = -1/2
    
    kernels = np.zeros(shape=(8,3,3))
    for rot in range(4):
        pk = np.rot90(pkb, k=rot)
        dk = np.rot90(dkb, k=rot)
        kernels[rot,:,:] = pk
        kernels[rot+4,:,:] = dk
    return kernels