numpy.fft.ifft2#
- fft.ifft2(a, s=None, axes=(-2, -1), norm=None, out=None)[source]#
Compute the 2-dimensional inverse discrete Fourier Transform.
This function computes the inverse of the 2-dimensional discrete Fourier Transform over any number of axes in an M-dimensional array by means of the Fast Fourier Transform (FFT). In other words,
ifft2(fft2(a)) == a
to within numerical accuracy. By default, the inverse transform is computed over the last two axes of the input array.The input, analogously to
ifft
, should be ordered in the same way as is returned byfft2
, i.e. it should have the term for zero frequency in the low-order corner of the two axes, the positive frequency terms in the first half of these axes, the term for the Nyquist frequency in the middle of the axes and the negative frequency terms in the second half of both axes, in order of decreasingly negative frequency.- Parameters:
- aarray_like
Input array, can be complex.
- ssequence of ints, optional
Shape (length of each axis) of the output (
s[0]
refers to axis 0,s[1]
to axis 1, etc.). This corresponds to n forifft(x, n)
. Along each axis, if the given shape is smaller than that of the input, the input is cropped. If it is larger, the input is padded with zeros.Changed in version 2.0: If it is
-1
, the whole input is used (no padding/trimming).If s is not given, the shape of the input along the axes specified by axes is used. See notes for issue on
ifft
zero padding.Deprecated since version 2.0: If s is not
None
, axes must not beNone
either.Deprecated since version 2.0: s must contain only
int
s, notNone
values.None
values currently mean that the default value forn
is used in the corresponding 1-D transform, but this behaviour is deprecated.- axessequence of ints, optional
Axes over which to compute the FFT. If not given, the last two axes are used. A repeated index in axes means the transform over that axis is performed multiple times. A one-element sequence means that a one-dimensional FFT is performed. Default:
(-2, -1)
.Deprecated since version 2.0: If s is specified, the corresponding axes to be transformed must not be
None
.- norm{“backward”, “ortho”, “forward”}, optional
Normalization mode (see
numpy.fft
). Default is “backward”. Indicates which direction of the forward/backward pair of transforms is scaled and with what normalization factor.New in version 1.20.0: The “backward”, “forward” values were added.
- outcomplex ndarray, optional
If provided, the result will be placed in this array. It should be of the appropriate shape and dtype for all axes (and hence is incompatible with passing in all but the trivial
s
).New in version 2.0.0.
- Returns:
- outcomplex ndarray
The truncated or zero-padded input, transformed along the axes indicated by axes, or the last two axes if axes is not given.
- Raises:
- ValueError
If s and axes have different length, or axes not given and
len(s) != 2
.- IndexError
If an element of axes is larger than than the number of axes of a.
See also
Notes
ifft2
is justifftn
with a different default for axes.See
ifftn
for details and a plotting example, andnumpy.fft
for definition and conventions used.Zero-padding, analogously with
ifft
, is performed by appending zeros to the input along the specified dimension. Although this is the common approach, it might lead to surprising results. If another form of zero padding is desired, it must be performed beforeifft2
is called.Examples
>>> import numpy as np >>> a = 4 * np.eye(4) >>> np.fft.ifft2(a) array([[1.+0.j, 0.+0.j, 0.+0.j, 0.+0.j], # may vary [0.+0.j, 0.+0.j, 0.+0.j, 1.+0.j], [0.+0.j, 0.+0.j, 1.+0.j, 0.+0.j], [0.+0.j, 1.+0.j, 0.+0.j, 0.+0.j]])