root/samples/cpp/dft.cpp

DEFINITIONS

1. help
2. main

#include "opencv2/core.hpp"
#include "opencv2/core/utility.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/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 ../data/lena.jpg]\n");
}

const char* keys =
{
    "{@image|../data/lena.jpg|input image file}"
};

int main(int argc, const char ** argv)
{
    help();
    CommandLineParser parser(argc, argv, keys);
    string filename = parser.get<string>(0);

    Mat img = imread(filename.c_str(), IMREAD_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, NORM_MINMAX);

    imshow("spectrum magnitude", mag);
    waitKey();
    return 0;
}