scipy.ndimage.geometric_transform#
- scipy.ndimage.geometric_transform(input, mapping, output_shape=None, output=None, order=3, mode='constant', cval=0.0, prefilter=True, extra_arguments=(), extra_keywords={})[source]#
Apply an arbitrary geometric transform.
The given mapping function is used to find, for each point in the output, the corresponding coordinates in the input. The value of the input at those coordinates is determined by spline interpolation of the requested order.
- Parameters:
- inputarray_like
The input array.
- mapping{callable, scipy.LowLevelCallable}
A callable object that accepts a tuple of length equal to the output array rank, and returns the corresponding input coordinates as a tuple of length equal to the input array rank.
- output_shapetuple of ints, optional
Shape tuple.
- outputarray or dtype, optional
The array in which to place the output, or the dtype of the returned array. By default an array of the same dtype as input will be created.
- orderint, optional
The order of the spline interpolation, default is 3. The order has to be in the range 0-5.
- mode{‘reflect’, ‘grid-mirror’, ‘constant’, ‘grid-constant’, ‘nearest’, ‘mirror’, ‘grid-wrap’, ‘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 (see additional plots and details on boundary modes):
- ‘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. This mode is also sometimes referred to as half-sample symmetric.
- ‘grid-mirror’
This is a synonym for ‘reflect’.
- ‘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. No interpolation is performed beyond the edges of the input.
- ‘grid-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. Interpolation occurs for samples outside the input’s extent as well.
- ‘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. This mode is also sometimes referred to as whole-sample symmetric.
- ‘grid-wrap’ (a b c d | a b c d | a b c d)
The input is extended by wrapping around to the opposite edge.
- ‘wrap’ (d b c d | a b c d | b c a b)
The input is extended by wrapping around to the opposite edge, but in a way such that the last point and initial point exactly overlap. In this case it is not well defined which sample will be chosen at the point of overlap.
- cvalscalar, optional
Value to fill past edges of input if mode is ‘constant’. Default is 0.0.
- prefilterbool, optional
Determines if the input array is prefiltered with
spline_filter
before interpolation. The default is True, which will create a temporary float64 array of filtered values if order > 1. If setting this to False, the output will be slightly blurred if order > 1, unless the input is prefiltered, i.e. it is the result of callingspline_filter
on the original input.- extra_argumentstuple, optional
Extra arguments passed to mapping.
- extra_keywordsdict, optional
Extra keywords passed to mapping.
- Returns:
- outputndarray
The filtered input.
See also
Notes
This function also accepts low-level callback functions with one the following signatures and wrapped in
scipy.LowLevelCallable
:int mapping(npy_intp *output_coordinates, double *input_coordinates, int output_rank, int input_rank, void *user_data) int mapping(intptr_t *output_coordinates, double *input_coordinates, int output_rank, int input_rank, void *user_data)
The calling function iterates over the elements of the output array, calling the callback function at each element. The coordinates of the current output element are passed through
output_coordinates
. The callback function must return the coordinates at which the input must be interpolated ininput_coordinates
. The rank of the input and output arrays are given byinput_rank
andoutput_rank
respectively.user_data
is the data pointer provided toscipy.LowLevelCallable
as-is.The callback function must return an integer error status that is zero if something went wrong and one otherwise. If an error occurs, you should normally set the Python error status with an informative message before returning, otherwise a default error message is set by the calling function.
In addition, some other low-level function pointer specifications are accepted, but these are for backward compatibility only and should not be used in new code.
For complex-valued input, this function transforms the real and imaginary components independently.
New in version 1.6.0: Complex-valued support added.
Examples
>>> import numpy as np >>> from scipy.ndimage import geometric_transform >>> a = np.arange(12.).reshape((4, 3)) >>> def shift_func(output_coords): ... return (output_coords[0] - 0.5, output_coords[1] - 0.5) ... >>> geometric_transform(a, shift_func) array([[ 0. , 0. , 0. ], [ 0. , 1.362, 2.738], [ 0. , 4.812, 6.187], [ 0. , 8.263, 9.637]])
>>> b = [1, 2, 3, 4, 5] >>> def shift_func(output_coords): ... return (output_coords[0] - 3,) ... >>> geometric_transform(b, shift_func, mode='constant') array([0, 0, 0, 1, 2]) >>> geometric_transform(b, shift_func, mode='nearest') array([1, 1, 1, 1, 2]) >>> geometric_transform(b, shift_func, mode='reflect') array([3, 2, 1, 1, 2]) >>> geometric_transform(b, shift_func, mode='wrap') array([2, 3, 4, 1, 2])