[SciPy-user] Explanation of different edge modes in scipy.ndimage

Stéfan van der Walt stefan@sun.ac...
Tue Nov 4 03:30:09 CST 2008


Hi Kurt

2008/10/31 Kurt Smith <kwmsmith@gmail.com>:
> I'm doing some gaussian filtering of periodic 2D arrays using
> scipy.ndimage.gaussian_filter.  There is a 'mode' argument that is set to
> 'reflect' by default.  In _ni_support.py:34 there is a conversion function,
> '_extend_mode_to_code' that gives the different modes available.  For
> periodic data I believe I should use 'wrap', but I'm interested to know what
> the other modes mean, esp the difference between 'reflect' and 'mirror'.
> For the record, the modes defined are 'nearest', 'wrap', 'reflect',
> 'mirror', and 'constant'.  For future reference, is there a place where
> these arguments are documented?

Sorry for the long overdue reply.

Reflect means:

1 | 2 | 3 | 2 | 1

While mirror means:

1 | 2 | 3 | 3| 2 | 1

(or the other way around, can't remember).

The problem with the last approach is the interpolation between 3 and
3, which is currently broken, so I'd advise against using it.

Thanks for your interest,

Regards
Stéfan


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