opencv/samples/cpp/dft.cpp

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char ** argv)
{
    const char* filename = argc >=2 ? argv[1] : "lena.jpg";

    Mat img = imread(filename, CV_LOAD_IMAGE_GRAYSCALE);
    if( img.empty() )
    {
        cout << "Usage: dft <image_name>" << endl;
        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;
}