[人工智能]opencv-core组件二之傅里叶变换

离散傅里叶变换

#include "opencv2/core.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
static void help(char ** argv)
{
    cout << endl
        <<  "This program demonstrated the use of the discrete Fourier transform (DFT). " << endl
        <<  "The dft of an image is taken and it's power spectrum is displayed."  << endl << endl
        <<  "Usage:"                                                                      << endl
        << argv[0] << " [image_name -- default lena.jpg]" << endl << endl;
}
int main(int argc,char**argv)
{
    help(argv);
    const char* filename=argc>=2?argv[1]:"lena.jpg";
    Mat I = imread( samples::findFile( filename ), IMREAD_GRAYSCALE);
    if( I.empty()){
        cout << "Error opening image" << endl;
        return EXIT_FAILURE;
    }
    Mat padded;
    int m=getOptimalDFTSize(I.rows);
    int n=getOptimalDFTSize(I.cols);
     //expand input image to optimal size,对于数字2、3、5的倍数的 图像大小，速度最快
    copyMakeBorder(I,padded,0,m-I.rows,0,n-I.cols,BORDER_CONSTANT,Scalar::all(0));
    //转为浮点型，并使用另一个通道将其展开以保存复值
    Mat planes[]={Mat_<float>(padded),Mat::zeros(padded.size().CV_32F)};
    Mat complexI;
    merge(planes,2,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))
    //分为实部和虚部
    split(complexI,planes);// planes[0] = Re(DFT(I), planes[1] = Im(DFT(I))
    magnitude(planes[0],planes[1],planes[0]);// planes[0] = magnitude
    Mat magI=planes[0];
    
    //对数变换，缩小范围便于显示
    magI+=Scalar::all(1);
    log(magI,magI);
    // crop the spectrum, if it has an odd number of rows or columns
    magI=magI(Rect(0,0,magI.cols&-2,magI.rows&-2));
    // rearrange the quadrants of Fourier image  so that the origin is at the image center
    int cx=magI.cols/2;
    int cy=magI.rows/2;
    Mat q0(magI, Rect(0, 0, cx, cy));   // Top-Left - Create a ROI per quadrant
    Mat q1(magI, Rect(cx, 0, cx, cy));  // Top-Right
    Mat q2(magI, Rect(0, 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, 0, 1, NORM_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 EXIT_SUCCESS;
}