OpenCV 离散傅立叶变换

 #include "opencv2/core/core.hpp"
 #include "opencv2/imgproc/imgproc.hpp"
 #include "opencv2/highgui/highgui.hpp"
 #include <iostream>
 int main(int argc, char ** argv)
 {
     const char* filename = argc >= ? argv[] : "lena.jpg";

     Mat I = imread(filename, CV_LOAD_IMAGE_GRAYSCALE);
     if( I.empty())
         return -;

     Mat padded;                            //expand input image to optimal size
     int m = getOptimalDFTSize( I.rows );
     int n = getOptimalDFTSize( I.cols ); // on the border add zero values
     copyMakeBorder(I, padded, , m - I.rows, , n - I.cols, BORDER_CONSTANT, Scalar::all());

     Mat planes[] = {Mat_<float>(padded), Mat::zeros(padded.size(), CV_32F)};
     Mat complexI;
     merge(planes, , complexI);         // Add to the expanded another plane with zeros

     dft(complexI, complexI);            // this way the result may fit in the source matrix

     // compute the magnitude and switch to logarithmic scale
     // => log(1 + sqrt(Re(DFT(I))^2 + Im(DFT(I))^2))
     split(complexI, planes);                   // planes[0] = Re(DFT(I), planes[1] = Im(DFT(I))
     magnitude(planes[], planes[], planes[]);// planes[0] = magnitude
     Mat magI = planes[];

     magI += Scalar::all();                    // switch to logarithmic scale
     log(magI, magI);

     // crop the spectrum, if it has an odd number of rows or columns
     magI = magI(Rect(, , magI.cols & -, magI.rows & -));

     // rearrange the quadrants of Fourier image  so that the origin is at the image center
     int cx = magI.cols/;
     int cy = magI.rows/;

     Mat q0(magI, Rect(, , cx, cy));   // Top-Left - Create a ROI per quadrant
     Mat q1(magI, Rect(cx, , cx, cy));  // Top-Right
     Mat q2(magI, Rect(, cy, cx, cy));  // Bottom-Left
     Mat q3(magI, Rect(cx, cy, cx, cy)); // Bottom-Right

     Mat tmp;                           // swap quadrants (Top-Left with Bottom-Right)
     q0.copyTo(tmp);
     q3.copyTo(q0);
     tmp.copyTo(q3);

     q1.copyTo(tmp);                    // swap quadrant (Top-Right with Bottom-Left)
     q2.copyTo(q1);
     tmp.copyTo(q2);

     normalize(magI, magI, , , CV_MINMAX); // Transform the matrix with float values into a
                                             // viewable image form (float between values 0 and 1).

     imshow("Input Image"       , I   );    // Show the result
     imshow("spectrum magnitude", magI);
     waitKey();

     return ;
 }