MATLAB Function Reference 
Twodimensional discrete Fourier transform
Syntax
Description
Y = fft2(X)
returns the twodimensional discrete Fourier transform (DFT) of X
, computed with a fast Fourier transform (FFT) algorithm. The result Y
is the same size as X.
Y = fft2(X,m,n)
truncates X
, or pads X
with zeros to create an m
byn
array before doing the transform. The result is m
byn
.
Algorithm
fft2(X)
can be simply computed as
This computes the onedimensional DFT of each column X
, then of each row of the result. The execution time for fft
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 fft2 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
fft2
supports inputs of data types double
and single
. If you call fft2
with the syntax y = fft2(X, ...)
, the output y
has the same data type as the input X
.
See Also
fft
, fftn
, fftw
, fftshift
, ifft2
fft  fftn 
© 19942005 The MathWorks, Inc.