opencv/samples/cpp/video_homography.cpp

/*
* video_homography.cpp
*
*  Created on: Oct 18, 2010
*      Author: erublee
*/

#include "opencv2/calib3d/calib3d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/features2d/features2d.hpp"
#include <iostream>
#include <list>
#include <vector>

using namespace std;
using namespace cv;

static void help(char **av)
{
    cout << "\nThis program demonstrated the use of features2d with the Fast corner detector and brief descriptors\n"
        << "to track planar objects by computing their homography from the key (training) image to the query (test) image\n\n" << endl;
    cout << "usage: " << av[0] << " <video device number>\n" << endl;
    cout << "The following keys do stuff:" << endl;
    cout << "  t : grabs a reference frame to match against" << endl;
    cout << "  l : makes the reference frame new every frame" << endl;
    cout << "  q or escape: quit" << endl;
}

namespace
{
    void drawMatchesRelative(const vector<KeyPoint>& train, const vector<KeyPoint>& query,
        std::vector<cv::DMatch>& matches, Mat& img, const vector<unsigned char>& mask = vector<
        unsigned char> ())
    {
        for (int i = 0; i < (int)matches.size(); i++)
        {
            if (mask.empty() || mask[i])
            {
                Point2f pt_new = query[matches[i].queryIdx].pt;
                Point2f pt_old = train[matches[i].trainIdx].pt;

                cv::line(img, pt_new, pt_old, Scalar(125, 255, 125), 1);
                cv::circle(img, pt_new, 2, Scalar(255, 0, 125), 1);

            }
        }
    }

    //Takes a descriptor and turns it into an xy point
    void keypoints2points(const vector<KeyPoint>& in, vector<Point2f>& out)
    {
        out.clear();
        out.reserve(in.size());
        for (size_t i = 0; i < in.size(); ++i)
        {
            out.push_back(in[i].pt);
        }
    }

    //Takes an xy point and appends that to a keypoint structure
    void points2keypoints(const vector<Point2f>& in, vector<KeyPoint>& out)
    {
        out.clear();
        out.reserve(in.size());
        for (size_t i = 0; i < in.size(); ++i)
        {
            out.push_back(KeyPoint(in[i], 1));
        }
    }

    //Uses computed homography H to warp original input points to new planar position
    void warpKeypoints(const Mat& H, const vector<KeyPoint>& in, vector<KeyPoint>& out)
    {
        vector<Point2f> pts;
        keypoints2points(in, pts);
        vector<Point2f> pts_w(pts.size());
        Mat m_pts_w(pts_w);
        perspectiveTransform(Mat(pts), m_pts_w, H);
        points2keypoints(pts_w, out);
    }

    //Converts matching indices to xy points
    void matches2points(const vector<KeyPoint>& train, const vector<KeyPoint>& query,
        const std::vector<cv::DMatch>& matches, std::vector<cv::Point2f>& pts_train,
        std::vector<Point2f>& pts_query)
    {

        pts_train.clear();
        pts_query.clear();
        pts_train.reserve(matches.size());
        pts_query.reserve(matches.size());

        size_t i = 0;

        for (; i < matches.size(); i++)
        {

            const DMatch & dmatch = matches[i];

            pts_query.push_back(query[dmatch.queryIdx].pt);
            pts_train.push_back(train[dmatch.trainIdx].pt);

        }

    }

    void resetH(Mat&H)
    {
        H = Mat::eye(3, 3, CV_32FC1);
    }
}

int main(int ac, char ** av)
{

    if (ac != 2)
    {
        help(av);
        return 1;
    }

    BriefDescriptorExtractor brief(32);

    VideoCapture capture;
    capture.open(atoi(av[1]));
    if (!capture.isOpened())
    {
        help(av);
        cout << "capture device " << atoi(av[1]) << " failed to open!" << endl;
        return 1;
    }

    cout << "following keys do stuff:" << endl;
    cout << "t : grabs a reference frame to match against" << endl;
    cout << "l : makes the reference frame new every frame" << endl;
    cout << "q or escape: quit" << endl;

    Mat frame;

    vector<DMatch> matches;

    BFMatcher desc_matcher(NORM_HAMMING);

    vector<Point2f> train_pts, query_pts;
    vector<KeyPoint> train_kpts, query_kpts;
    vector<unsigned char> match_mask;

    Mat gray;

    bool ref_live = true;

    Mat train_desc, query_desc;
    const int DESIRED_FTRS = 500;
    GridAdaptedFeatureDetector detector(new FastFeatureDetector(10, true), DESIRED_FTRS, 4, 4);

    Mat H_prev = Mat::eye(3, 3, CV_32FC1);
    for (;;)
    {
        capture >> frame;
        if (frame.empty())
            break;

        cvtColor(frame, gray, CV_RGB2GRAY);

        detector.detect(gray, query_kpts); //Find interest points

        brief.compute(gray, query_kpts, query_desc); //Compute brief descriptors at each keypoint location

        if (!train_kpts.empty())
        {

            vector<KeyPoint> test_kpts;
            warpKeypoints(H_prev.inv(), query_kpts, test_kpts);

            Mat mask = windowedMatchingMask(test_kpts, train_kpts, 25, 25);
            desc_matcher.match(query_desc, train_desc, matches, mask);
            drawKeypoints(frame, test_kpts, frame, Scalar(255, 0, 0), DrawMatchesFlags::DRAW_OVER_OUTIMG);

            matches2points(train_kpts, query_kpts, matches, train_pts, query_pts);

            if (matches.size() > 5)
            {
                Mat H = findHomography(train_pts, query_pts, RANSAC, 4, match_mask);
                if (countNonZero(Mat(match_mask)) > 15)
                {
                    H_prev = H;
                }
                else
                    resetH(H_prev);
                drawMatchesRelative(train_kpts, query_kpts, matches, frame, match_mask);
            }
            else
                resetH(H_prev);

        }
        else
        {
            H_prev = Mat::eye(3, 3, CV_32FC1);
            Mat out;
            drawKeypoints(gray, query_kpts, out);
            frame = out;
        }

        imshow("frame", frame);

        if (ref_live)
        {
            train_kpts = query_kpts;
            query_desc.copyTo(train_desc);
        }
        char key = (char)waitKey(2);
        switch (key)
        {
        case 'l':
            ref_live = true;
            resetH(H_prev);
            break;
        case 't':
            ref_live = false;
            train_kpts = query_kpts;
            query_desc.copyTo(train_desc);
            resetH(H_prev);
            break;
        case 27:
        case 'q':
            return 0;
            break;
        }

    }
    return 0;
}