MATLAB Function Reference

fftshift

Shift zero-frequency component of fast Fourier transform to center of spectrum

Syntax

Y = fftshift(X)
Y = fftshift(X,dim)

Description

Y = fftshift(X) rearranges the outputs of fft, fft2, and fftn by moving the zero-frequency component to the center of the array. It is useful for visualizing a Fourier transform with the zero-frequency component in the middle of the spectrum.

For vectors, fftshift(X) swaps the left and right halves of X. For matrices, fftshift(X) swaps quadrants one and three of X with quadrants two and four. For higher-dimensional arrays, fftshift(X) swaps "half-spaces" of X along each dimension.

Y = fftshift(X,dim) applies the fftshift operation along the dimension dim.

Examples

For any matrix X

Y = fft2(X)

has Y(1,1) = sum(sum(X)); the zero-frequency component of the signal is in the upper-left corner of the two-dimensional FFT. For

Z = fftshift(Y)

this zero-frequency component is near the center of the matrix.

See Also

fft, fft2, fftn, ifftshift

fftn

fgetl