MATLAB Function Reference 
Twodimensional inverse discrete Fourier transform
Syntax
Description
Y = ifft2(X)
returns the twodimensional inverse discrete Fourier transform (DFT) of X
, computed with a fast Fourier transform (FFT) algorithm. The result Y
is the same size as X.
ifft2
tests X
to see whether it is conjugate symmetric. If so, the computation is faster and the output is real. An M
byN
matrix X
is conjugate symmetric if X(i,j) = conj(X(mod(Mi+1, M) + 1, mod(Nj+1, N) + 1))
for each element of X
.
Y = ifft2(X,m,n)
returns the m
byn
inverse fast Fourier transform of matrix X
.
y = ifft2(..., 'symmetric')
causes ifft2
to treat X
as conjugate symmetric. This option is useful when X
is not exactly conjugate symmetric, merely because of roundoff error.
y = ifft2(..., 'nonsymmetric')
is the same as calling ifft2(...)
without the argument 'nonsymmetric'
.
For any X
, ifft2(fft2(X))
equals X
to within roundoff error.
Algorithm
The algorithm for ifft2(X)
is the same as the algorithm for fft2(X)
, except for a sign change and scale factors of [m,n]
=
size(X)
. The execution time for ifft2
depends on the length of the transform. It is fastest for powers of two. It is almost as fast for lengths that have only small prime factors. It is typically several times slower for lengths that are prime or which have large prime factors.
Note
You might be able to increase the speed of ifft2 using the utility function fftw , which controls how MATLAB optimizes the algorithm used to compute an FFT of a particular size and dimension.

Data Type Support
ifft2
supports inputs of data types double
and single
. If you call ifft2
with the syntax y = ifft2(X, ...)
, the output y
has the same data type as the input X
.
See Also
dftmtx
and freqz
in the Signal Processing Toolbox, and:
fft2
, fftw
, fftshift
, ifft
, ifftn
, ifftshift
ifft  ifftn 
© 19942005 The MathWorks, Inc.