main.cpp

#include <iostream>
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/nonfree/nonfree.hpp"

using namespace std;
using namespace cv;

// credits to
// https://jayrambhia.wordpress.com/2012/09/24/sift-based-tracker/
// http://www.jayrambhia.com/blog/selecting-roibb-in-opencvmat/

Point point1, point2;
int drag = 0;
Rect rect;
Mat img, roiImg;
int select_flag = 0;
vector<KeyPoint> keypoints_roi, keypoints_img;
Mat descriptor_roi, descriptor_img;
SIFT sift;

void mouseHandler(int event, int x, int y, int flags, void* param)
{
    if (event == CV_EVENT_LBUTTONDOWN && !drag)
    {
        point1 = Point(x, y);
        drag = 1;
    }

    if (event == CV_EVENT_MOUSEMOVE && drag)
    {
        Mat img1 = img.clone();
        point2 = Point(x, y);
        rectangle(img1, point1, point2, CV_RGB(255, 0, 0), 3, 8, 0);
        imshow("image", img1);
    }

    if (event == CV_EVENT_LBUTTONUP && drag)
    {
        point2 = Point(x, y);
        int width = abs(x-point1.x);
        int height = abs(y-point1.y);
        Point begin = point1;
        if(point1.x>point2.x) {
          begin = point2;
        }
        if(begin.x + width >= img.size().width) {
          width = img.size().width-begin.x;
        }
        if(begin.y + height >= img.size().height) {
          height = img.size().height-begin.y;
        }

        rect = Rect(begin.x, begin.y,
                    width, height);
        drag = 0;
        roiImg = img(rect);
        roiImg = roiImg.clone();
        sift(roiImg, Mat(), keypoints_roi, descriptor_roi);
        drawKeypoints(roiImg, keypoints_roi, roiImg,
                      Scalar::all(-1),
                      DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS & DrawMatchesFlags::DRAW_RICH_KEYPOINTS);
    }

    if (event == CV_EVENT_LBUTTONUP)
    {
        /* ROI selected */
        select_flag = 1;
        drag = 0;
    }
}


int main(int argc, char **argv) {
    VideoCapture cap(0);

    if ( !cap.isOpened() )  // if not success, exit program
    {
        cout << "Cannot open the web cam" << endl;
        return -1;
    }

    namedWindow("image", CV_WINDOW_AUTOSIZE);
    namedWindow("ROI", CV_WINDOW_AUTOSIZE);


    while(true) {
        Mat descriptors;
        vector<KeyPoint> keypoints;
        cap.read(img);

        cvSetMouseCallback("image", mouseHandler, NULL);

        if (select_flag == 1)
        {
            imshow("ROI", roiImg); /* show the image bounded by the box */
            sift(img, Mat(), keypoints_img, descriptor_img);
            FlannBasedMatcher matcher;
            vector<DMatch> matches;
            matcher.match(descriptor_roi, descriptor_img, matches);
            vector<DMatch> good_matches;
            double min = 200.0;
            for (int i=0; i<descriptor_roi.rows; i++)
            {
                if(matches[i].distance < min)
                {
                    good_matches.push_back(matches[i]);
                }
            }
            vector<KeyPoint> keypoints1;
            for (int i=0; i<good_matches.size(); i++)
            {
                keypoints1.push_back(keypoints_img[good_matches[i].trainIdx]);
            }
            drawKeypoints(img, keypoints1, img,
                          Scalar::all(-1),
                          DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS & DrawMatchesFlags::DRAW_RICH_KEYPOINTS);
        }

        imshow("image", img);

        if (waitKey(30) == 27) {
            cout << "esc key is pressed by user" << endl;
            break;
        }
    }

    return 0;
}