example_18-01.cpp

// Example 18-1. Reading a chessboard’s width and height, reading and collecting
// the requested number of views, and calibrating the camera
#include <iostream>
#include <opencv2/opencv.hpp>

using std::vector;
using std::cout;
using std::cerr;
using std::endl;

void help(char **argv) {  // todo rewrite this
    cout << "\n\n"
         << "Example 18-1:\nReading a chessboard’s width and height,\n"
         << "              reading and collecting the requested number of views,\n" 
         << "              and calibrating the camera\n\n" 
         << "Call:\n" << argv[0] << " <board_width> <board_height> <number_of_boards> <if_video,_delay_between_framee_capture> <image_scaling_factor>\n\n"
         << "Example:\n" << argv[0] << " 9 6 15 500 0.5\n"
         << "-- to use the checkerboard9x6.png provided\n\n"
         << " * First it reads in checker boards and calibrates itself\n" 
         << " * Then it saves and reloads the calibration matricies\n"
         << " * Then it creates an undistortion map and finally\n"
         << " * It displays an undistorted image\n"
         << endl;
}

int main(int argc, char *argv[]) {
    int n_boards = 0;           // will be set by input list
    float image_sf = 0.5f;      // image scaling factor
    float delay = 1.f;
    int board_w = 0;
    int board_h = 0;

    if (argc < 4 || argc > 6) {
        cout << "\nERROR: Wrong number of input parameters\n";
        help(argv);
        return -1;
    }

    board_w = atoi(argv[1]);
    board_h = atoi(argv[2]);
    n_boards = atoi(argv[3]);

    if (argc > 4) {
        delay = atof(argv[4]);
    }
    if (argc > 5) {
        image_sf = atof(argv[5]);
    }

    int board_n = board_w * board_h;
    cv::Size board_sz = cv::Size(board_w, board_h);
    cv::VideoCapture capture(0);
    if (!capture.isOpened()) {
        cout << "\nCouldn't open the camera\n";
        help(argv);
        return -1;
    }

    // ALLOCATE STORAGE
    //
    vector<vector<cv::Point2f> > image_points;
    vector<vector<cv::Point3f> > object_points;

    // Capture corner views: loop until we've got n_boards successful
    // captures (all corners on the board are found).
    //
    double last_captured_timestamp = 0;
    cv::Size image_size;
    while (image_points.size() < (size_t)n_boards) {
    cv::Mat image0, image;
    capture >> image0;
    image_size = image0.size();
    cv::resize(image0, image, cv::Size(), image_sf, image_sf, cv::INTER_LINEAR);

    // Find the board
    //
    vector<cv::Point2f> corners;
    bool found = cv::findChessboardCorners(image, board_sz, corners);

    // Draw it
    //
    drawChessboardCorners(image, board_sz, corners, found);

    // If we got a good board, add it to our data
    //
    double timestamp = static_cast<double>(clock()) / CLOCKS_PER_SEC;
    if (found && timestamp - last_captured_timestamp > 1) {
        last_captured_timestamp = timestamp;
        image ^= cv::Scalar::all(255);
        cv::Mat mcorners(corners);

        // do not copy the data
        mcorners *= (1.0 / image_sf);

        // scale the corner coordinates
        image_points.push_back(corners);
        object_points.push_back(vector<cv::Point3f>());
        vector<cv::Point3f> &opts = object_points.back();

        opts.resize(board_n);
        for (int j = 0; j < board_n; j++) {
            opts[j] = cv::Point3f(static_cast<float>(j / board_w),
                                  static_cast<float>(j % board_w), 0.0f);
        }
        cout << "Collected our " << static_cast<uint>(image_points.size())
             << " of " << n_boards << " needed chessboard images\n" << endl;
    }
    cv::imshow("Calibration", image);

    // show in color if we did collect the image
    if ((cv::waitKey(30) & 255) == 27)
      return -1;
    }

    // END COLLECTION WHILE LOOP.
    cv::destroyWindow("Calibration");
    cout << "\n\n*** CALIBRATING THE CAMERA...\n" << endl;

    // CALIBRATE THE CAMERA!
    //
    cv::Mat intrinsic_matrix, distortion_coeffs;
    double err = cv::calibrateCamera(
        object_points, image_points, image_size, intrinsic_matrix,
        distortion_coeffs, cv::noArray(), cv::noArray(),
        cv::CALIB_ZERO_TANGENT_DIST | cv::CALIB_FIX_PRINCIPAL_POINT);

    // SAVE THE INTRINSICS AND DISTORTIONS
    cout << " *** DONE!\n\nReprojection error is " << err
         << "\nStoring Intrinsics.xml and Distortions.xml files\n\n";
    cv::FileStorage fs("intrinsics.xml", cv::FileStorage::WRITE);
    fs << "image_width" << image_size.width << "image_height" << image_size.height
       << "camera_matrix" << intrinsic_matrix << "distortion_coefficients"
       << distortion_coeffs;
    fs.release();

    // EXAMPLE OF LOADING THESE MATRICES BACK IN:
    fs.open("intrinsics.xml", cv::FileStorage::READ);
    cout << "\nimage width: " << static_cast<int>(fs["image_width"]);
    cout << "\nimage height: " << static_cast<int>(fs["image_height"]);
    cv::Mat intrinsic_matrix_loaded, distortion_coeffs_loaded;
    fs["camera_matrix"] >> intrinsic_matrix_loaded;
    fs["distortion_coefficients"] >> distortion_coeffs_loaded;
    cout << "\nintrinsic matrix:" << intrinsic_matrix_loaded;
    cout << "\ndistortion coefficients: " << distortion_coeffs_loaded << endl;

    // Build the undistort map which we will use for all
    // subsequent frames.
    //
    cv::Mat map1, map2;
    cv::initUndistortRectifyMap(intrinsic_matrix_loaded, distortion_coeffs_loaded,
                              cv::Mat(), intrinsic_matrix_loaded, image_size,
                              CV_16SC2, map1, map2);

    // Just run the camera to the screen, now showing the raw and
    // the undistorted image.
    //
    for (;;) {
        cv::Mat image, image0;
        capture >> image0;

        if (image0.empty()) {
            break;
        }
        cv::remap(image0, image, map1, map2, cv::INTER_LINEAR,
            cv::BORDER_CONSTANT, cv::Scalar());
        cv::imshow("Undistorted", image);
        if ((cv::waitKey(30) & 255) == 27) {
            break;
        }
    }

    return 0;
}