How exactly does the “reflect” mode for scipys ndimage filters work?

Question

I\'m failing to understand exactly how the reflect mode handles my arrays. I have this very simple array:

import numpy as np
from scipy.ndimage.filters impor         


        

Answer 1

Suppose the data in one axis is 1 2 3 4 5 6 7 8. The following table shows how the data is extended for each mode (assuming cval=0):

    mode       |   Ext   |         Input          |   Ext
    -----------+---------+------------------------+---------
    'mirror'   | 4  3  2 | 1  2  3  4  5  6  7  8 | 7  6  5
    'reflect'  | 3  2  1 | 1  2  3  4  5  6  7  8 | 8  7  6
    'nearest'  | 1  1  1 | 1  2  3  4  5  6  7  8 | 8  8  8
    'constant' | 0  0  0 | 1  2  3  4  5  6  7  8 | 0  0  0
    'wrap'     | 6  7  8 | 1  2  3  4  5  6  7  8 | 1  2  3

For an even window size n, consider the window of size n+1, and then don't include the lower and right edges. (The position of the window can be changed by using the origin argument.)