scipy.ndimage.spline_filter1d(input, order=3, axis=-1, output=<class 'numpy.float64'>, mode='mirror')[source]

Calculate a one-dimensional spline filter along the given axis.

The lines of the array along the given axis are filtered by a spline filter. The order of the spline must be >= 2 and <= 5.

input : array_like

The input array.

order : int, optional

The order of the spline, default is 3.

axis : int, optional

The axis along which the spline filter is applied. Default is the last axis.

output : ndarray or dtype, optional

The array in which to place the output, or the dtype of the returned array. Default is numpy.float64.

mode : {‘reflect’, ‘constant’, ‘nearest’, ‘mirror’, ‘wrap’}, optional

The mode parameter determines how the input array is extended beyond its boundaries. Default is ‘constant’. Behavior for each valid value is as follows:

‘reflect’ (d c b a | a b c d | d c b a)

The input is extended by reflecting about the edge of the last pixel.

‘constant’ (k k k k | a b c d | k k k k)

The input is extended by filling all values beyond the edge with the same constant value, defined by the cval parameter.

‘nearest’ (a a a a | a b c d | d d d d)

The input is extended by replicating the last pixel.

‘mirror’ (d c b | a b c d | c b a)

The input is extended by reflecting about the center of the last pixel.

‘wrap’ (a b c d | a b c d | a b c d)

The input is extended by wrapping around to the opposite edge.

spline_filter1d : ndarray

The filtered input.


All functions in ndimage.interpolation do spline interpolation of the input image. If using b-splines of order > 1, the input image values have to be converted to b-spline coefficients first, which is done by applying this one-dimensional filter sequentially along all axes of the input. All functions that require b-spline coefficients will automatically filter their inputs, a behavior controllable with the prefilter keyword argument. For functions that accept a mode parameter, the result will only be correct if it matches the mode used when filtering.

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