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fftshift
Move zero'th lag to center of spectrum.
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.
For any matrix 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 One-dimensional fast Fourier transform
fft2 Two-dimensional fast Fourier transform