>>> y = np.arange(28).reshape(4,7)
>>> y
array([[ 0, 1, 2, 3, 4, 5, 6],
[ 7, 8, 9, 10, 11, 12, 13],
[14, 15, 16, 17, 18, 19, 20],
[21, 22, 23, 24, 25, 26, 27]])
>>> y[::2, ::3]
array([[ 0, 3, 6],
[14, 17, 20]])
>>> y
array([[ 0, 1, 2, 3, 4, 5, 6],
[ 7, 8, 9, 10, 11, 12, 13],
[14, 15, 16, 17, 18, 19, 20],
[21, 22, 23, 24, 25, 26, 27]])
>>> y[::, ::2]
array([[ 0, 2, 4, 6],
[ 7, 9, 11, 13],
[14, 16, 18, 20],
[21, 23, 25, 27]])