text: #include "opencv2/core/core.hpp"
  #include "opencv2/imgproc/imgproc.hpp"
  #include "opencv2/highgui/highgui.hpp"
  
  #include <stdio.h>
  
  using namespace cv;
  using namespace std;
  
  static void help()
  {
      printf("\nThis program demonstrated the use of the discrete Fourier transform (dft)\n"
             "The dft of an image is taken and it's power spectrum is displayed.\n"
             "Usage:\n"
              "./dft [image_name -- default lena.jpg]\n");
  }
  
  const char* keys =
  {
      "{1| |lena.jpg|input image file}"
  };
  
  int main(int argc, const char ** argv)
  {
      help();
      CommandLineParser parser(argc, argv, keys);
      string filename = parser.get<string>("1");
  
      Mat img = imread(filename.c_str(), CV_LOAD_IMAGE_GRAYSCALE);
      if( img.empty() )
      {
          help();
          printf("Cannot read image file: %s\n", filename.c_str());
          return -1;
      }
      int M = getOptimalDFTSize( img.rows );
      int N = getOptimalDFTSize( img.cols );
      Mat padded;
      copyMakeBorder(img, padded, 0, M - img.rows, 0, N - img.cols, BORDER_CONSTANT, Scalar::all(0));
  
      Mat planes[] = {Mat_<float>(padded), Mat::zeros(padded.size(), CV_32F)};
      Mat complexImg;
      merge(planes, 2, complexImg);
  
      dft(complexImg, complexImg);
  
      // compute log(1 + sqrt(Re(DFT(img))**2 + Im(DFT(img))**2))
      split(complexImg, planes);
      magnitude(planes[0], planes[1], planes[0]);
      Mat mag = planes[0];
      mag += Scalar::all(1);
      log(mag, mag);
  
      // crop the spectrum, if it has an odd number of rows or columns
      mag = mag(Rect(0, 0, mag.cols & -2, mag.rows & -2));
  
      int cx = mag.cols/2;
      int cy = mag.rows/2;
  
      // rearrange the quadrants of Fourier image
      // so that the origin is at the image center
      Mat tmp;
      Mat q0(mag, Rect(0, 0, cx, cy));
      Mat q1(mag, Rect(cx, 0, cx, cy));
      Mat q2(mag, Rect(0, cy, cx, cy));
      Mat q3(mag, Rect(cx, cy, cx, cy));
  
      q0.copyTo(tmp);
      q3.copyTo(q0);
      tmp.copyTo(q3);
  
      q1.copyTo(tmp);
      q2.copyTo(q1);
      tmp.copyTo(q2);
  
      normalize(mag, mag, 0, 1, CV_MINMAX);
  
      imshow("spectrum magnitude", mag);
      waitKey();
      return 0;
  }
  