How can I remove the lowest n frequencies of an image? Are the lower frequencies around the centre of the FFT result?

  • $\begingroup$ I would say the lower left corner is the DC. You can test by creating a 2D sine signal and run the FFT. $\endgroup$ – Moti Oct 12 '15 at 4:29
  • $\begingroup$ Let's say I use fftshift to put the DC component in the centre. How could I select exactly n frequencies? Can I just use a circular mask on the FFT result to remove the lowest n frequencies? But how to I adjust the radius? $\endgroup$ – Bgt Oct 12 '15 at 13:16
  • $\begingroup$ In the 2D FFT, every point represents a 1D wave with a direct according to point, a frequency according to the distance from the origin, and a phase based on your reference position on the wave. Now, the mask you want to use, do it around the origin. Why you need the shifting? $\endgroup$ – Moti Oct 13 '15 at 15:22

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