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Hi, I have calibrated the camera of my LG phone using 30 checkerboard images. I have checked the found corners on the calibration images one by one, they are ok, on the right place between the squares. But when I use the camera intrinsic matrix, and the distortion coefficient matrix( which I obtained by the calibrateCamera() function) to undistort an image I get strange results.

Original image:

"undistorted" image:

the calibration code snippet :

void calibrateCamera(vector<string> imagefilePaths){
  int numBoards = 30;
  int numCornersHor = 9;
  int numCornersVer = 7;

  vector<vector<Point3f>> object_points;
  vector<vector<Point2f>> image_points;

  vector<Point2f> corners;
  vector<Point3f> obj;
  int numSquares = numCornersHor * numCornersVer;
  Size board_sz = Size(numCornersHor, numCornersVer);
  float scale =0.04;

  for(int j=0;j<numSquares;j++){
        obj.push_back(Point3f( (j/numCornersHor)*scale , (j%numCornersHor)*scale, 0.0f));
  }

  Mat image;

  for(int i = 0; i < imagefilePaths.size(); i++ ){
    image = imread( imagefilePaths[i], IMREAD_COLOR);
    Mat gray_image;
    cvtColor(image, gray_image, CV_BGR2GRAY);

    bool found = findChessboardCorners(image, board_sz, corners, CV_CALIB_CB_ADAPTIVE_THRESH | CV_CALIB_CB_FILTER_QUADS);

    if(found){
      cornerSubPix(gray_image, corners, Size(11, 11), Size(-1, -1), TermCriteria(CV_TERMCRIT_EPS | CV_TERMCRIT_ITER, 30, 0.1));
      drawChessboardCorners(gray_image, board_sz, corners, found);
    }

    imwrite( ("/home/gabor/cpp/ocv_test/chess_" + to_string(i) + ".jpg") , gray_image );
    //imshow("win2", gray_image);
    //int key = waitKey(1000);

    if(found!=0){
      image_points.push_back(corners);
      object_points.push_back(obj);
    }

  }

  Mat intrinsic = Mat(3, 3, CV_32FC1);
  Mat distCoeffs;
  vector<Mat> rvecs;
  vector<Mat> tvecs;

  calibrateCamera(object_points, image_points, image.size(), intrinsic, distCoeffs, rvecs, tvecs);

  /*FileStorage fs("/home/gabor/cpp/ocv_test/calibration/LGK5_.yml", FileStorage::WRITE);
  fs << "intrinsics" << intrinsic;
  fs << "distortion_coefficients" << distCoeffs;
  fs << "translation vectors" << tvecs;
  fs.release();
*/

}

Is it something with the corner finding parameters? Thanks.