title: Implement Gaussian high-pass filter by opencv with FFT
body: <p>I want to Implement the image enhancement according following paper like Figure 5.
  <a href="http://www.mdpi.com/1424-8220/11/12/11357/htm" rel="nofollow">http://www.mdpi.com/1424-8220/11/12/11357/htm</a></p>
  
  <p>I use opencv 2.4.9 to implement FFT as following  example code:
  <a href="http://docs.opencv.org/2.4/doc/tutorials/core/discrete_fourier_transform/discrete_fourier_transform.html" rel="nofollow">http://docs.opencv.org/2.4/doc/tutorials/core/discrete_fourier_transform/discrete_fourier_transform.html</a></p>
  
  <p>my question is how could I get the real and complex by the magnitude filtered by the Gaussian high-pass filter</p>