scipy.signal.order_filter

scipy.signal.order_filter(a, domain, rank)

Perform an order filter on an N-dimensional array.

Perform an order filter on the array in. The domain argument acts as a mask centered over each pixel. The non-zero elements of domain are used to select elements surrounding each input pixel which are placed in a list. The list is sorted, and the output for that pixel is the element corresponding to rank in the sorted list.

Parameters :

a : ndarray

The N-dimensional input array.

domain : array_like

A mask array with the same number of dimensions as in. Each dimension should have an odd number of elements.

rank : int

A non-negative integer which selects the element from the sorted list (0 corresponds to the smallest element, 1 is the next smallest element, etc.).

Returns :

out : ndarray

The results of the order filter in an array with the same shape as in.

Examples

>>> from scipy import signal
>>> x = np.arange(25).reshape(5, 5)
>>> domain = np.identity(3)
>>> x
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]])
>>> signal.order_filter(x, domain, 0)
array([[  0.,   0.,   0.,   0.,   0.],
       [  0.,   0.,   1.,   2.,   0.],
       [  0.,   5.,   6.,   7.,   0.],
       [  0.,  10.,  11.,  12.,   0.],
       [  0.,   0.,   0.,   0.,   0.]])
>>> signal.order_filter(x, domain, 2)
array([[  6.,   7.,   8.,   9.,   4.],
       [ 11.,  12.,  13.,  14.,   9.],
       [ 16.,  17.,  18.,  19.,  14.],
       [ 21.,  22.,  23.,  24.,  19.],
       [ 20.,  21.,  22.,  23.,  24.]])