scipy.ndimage.affine_transform

scipy.ndimage.affine_transform(input, matrix, offset=0.0, output_shape=None, output=None, order=3, mode='constant', cval=0.0, prefilter=True)

Apply an affine transformation.

The given matrix and offset are used to find for each point in the output the corresponding coordinates in the input by an affine transformation. The value of the input at those coordinates is determined by spline interpolation of the requested order. Points outside the boundaries of the input are filled according to the given mode.

If a two-dimensional array is supplied to the matrix parameter, given an output image pixel index vector o, the pixel value is determined from the input image at position np.dot(matrix,o) + offset.

A diagonal matrix can be specified by supplying a one-dimensional array-like to the matrix parameter, in which case a more efficient algorithm is applied.

Warning

Currently, the exact interpretation of the affine transformation depends on whether the matrix is supplied as a one-dimensional or two-dimensional array. This is considered a bug, and starting from scipy 0.18.0, the behaviour for one-dimensional matrix arguments will be modified to match the two-dimensional case.

Until then, if a one-dimensional array is supplied to the matrix parameter, the output pixel value at index o is determined from the input image at position matrix * (o + offset).

Parameters:

input : ndarray

The input array.

matrix : ndarray

The matrix must be two-dimensional or can also be given as a one-dimensional sequence or array. In the latter case, it is assumed that the matrix is diagonal. A more efficient algorithms is then applied that exploits the separability of the problem.

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 : ndarray or dtype, optional

The array in which to place the output, or the dtype of the returned array.

order : int, optional

The order of the spline interpolation, default is 3. The order has to be in the range 0-5.

mode : str, optional

Points outside the boundaries of the input are filled according to the given mode (‘constant’, ‘nearest’, ‘reflect’ or ‘wrap’). Default is ‘constant’.

cval : scalar, optional

Value used for points outside the boundaries of the input if mode='constant'. Default is 0.0

prefilter : bool, optional

The parameter prefilter determines if the input is pre-filtered with spline_filter before interpolation (necessary for spline interpolation of order > 1). If False, it is assumed that the input is already filtered. Default is True.

Returns:

affine_transform : ndarray or None

The transformed input. If output is given as a parameter, None is returned.