fft and fft2.
Y = fftshift(X)
Y = fftshift(X) rearranges the outputs of fft and fft2 by moving the zero frequency component to the center of the spectrum, which is sometimes a more convenient form.
If X is a vector, Y is a vector with the left and right halves swapped.
If X is a matrix, Y is a matrix with quadrants one and three swapped with quadrants two and four.
X
Y = fft2(X)
has Y(1,1) = sum(sum(X)); the DC component of the signal is in the upper-left corner of the two-dimensional FFT. For
Z = fftshift(Y)
this DC component is near the center of the matrix.
fft,fft2
(c) Copyright 1994 by The MathWorks, Inc.