Fourier power spectrum

See the FFT transform using different windowing techniques. 
Select a ROI in the left image simply by dragging the mouse. 

The fft algorithm uses a fast FFT method, based on images having dimensions of powers of 2. 

You can specify a windowing of the image prior to the fft, in order to remove spikes effects due to image edges discontinuities.

Both amplitude and phase of the spectrum can be seen:

You can even choose to reconstruct the image using information from the amplitude only, phase only, or both: