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phase spectrum

Where, spatially, each frequency component is positioned.

The phase spectrum \angle F(u,v) = \operatorname{atan2}(\operatorname{Im}(F(u,v)), \operatorname{Re}(F(u,v))) reports each frequency component's position -- shifting a pattern sideways changes phase at every frequency it appears in while leaving magnitude completely unchanged. Both spectra together are needed to reconstruct an image exactly.

See also

2D discrete Fourier transform magnitude spectrum
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