opencv sift match

#include "opencvlib.h"
using namespace cv;

int main()
{
    Mat img_1 = cv::imread("1.png");
    Mat img_2 = cv::imread("2.png");

    imshow("img1", img_1);
    imshow("img2", img_2);

    if (!img_1.data || !img_2.data)
    {
        std::cout << " --(!) Error reading images " << std::endl; return -1;
    }

    //-- Step 1: Detect the keypoints using SURF Detector
    int minHessian = 400;

    SurfFeatureDetector detector(minHessian);

    std::vector<KeyPoint> keypoints_1, keypoints_2;

    detector.detect(img_1, keypoints_1);
    detector.detect(img_2, keypoints_2);

    //-- Step 2: Calculate descriptors (feature vectors)
    SiftDescriptorExtractor extractor;
    //SurfDescriptorExtractor
    Mat descriptors_1, descriptors_2;

    extractor.compute(img_1, keypoints_1, descriptors_1);
    extractor.compute(img_2, keypoints_2, descriptors_2);

    //-- Step 3: Matching descriptor vectors using FLANN matcher
    FlannBasedMatcher matcher;
    std::vector< DMatch > matches;
    matcher.match(descriptors_1, descriptors_2, matches);

    double max_dist = 0; double min_dist = 1000;

    //-- Quick calculation of max and min distances between keypoints
    for (int i = 0; i < descriptors_1.rows; i++)
    {
        double dist = matches[i].distance;
        if (dist < min_dist) min_dist = dist;
        if (dist > max_dist) max_dist = dist;
    }

    printf("-- Max dist : %f \n", max_dist);
    printf("-- Min dist : %f \n", min_dist);

    //-- Draw only "good" matches (i.e. whose distance is less than 2*min_dist )
    //-- PS.- radiusMatch can also be used here.
    std::vector< DMatch > good_matches;

    for (int i = 0; i < descriptors_1.rows; i++)
    {
        if (matches[i].distance < 2 * min_dist)
        {
            good_matches.push_back(matches[i]);
        }
    }

    //-- Draw only "good" matches
    Mat img_matches;
    drawMatches(img_1, keypoints_1, img_2, keypoints_2,
        good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
        vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);

    //-- Show detected matches
    imshow("Good Matches", img_matches);
    imwrite("matchs.jpg", img_matches);

    for (int i = 0; i < good_matches.size(); i++)
    {
        printf("-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  \n", i, good_matches[i].queryIdx, good_matches[i].trainIdx);
    }

    waitKey(0);

    system("pause");

    return 0;
}

result