scipy.ndimage._interpolation:affine_transform

Parameters

input : array_like

The input array.

matrix : ndarray

The inverse coordinate transformation matrix, mapping output coordinates to input coordinates. If ndim is the number of dimensions of input, the given matrix must have one of the following shapes:

• (ndim, ndim): the linear transformation matrix for each output coordinate.

• (ndim,): assume that the 2-D transformation matrix is diagonal, with the diagonal specified by the given value. A more efficient algorithm is then used that exploits the separability of the problem.

• (ndim + 1, ndim + 1): assume that the transformation is specified using homogeneous coordinates ^[1]. In this case, any value passed to offset is ignored.

• (ndim, ndim + 1): as above, but the bottom row of a homogeneous transformation matrix is always [0, 0, ..., 1], and may be omitted.

offset : float or sequence, optional

The offset into the array where the transform is applied. If a float, offset is the same for each axis. If a sequence, offset should contain one value for each axis.

output_shape : tuple of ints, optional

Shape tuple.

output : array 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.

order : int, 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' (b c d b c | a b c d | b c a b c)

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.

For the example illustrated above, the edge values a and d overlap, while the inner pattern b c repeats. The example demonstrates one possible output, while b c a b c | a b c d | b c d b c is another, since either a or d may occur at each point of overlap.

cval : scalar, optional

Value to fill past edges of input if mode is 'constant'. Default is 0.0.

prefilter : bool, 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 calling spline_filter on the original input.