content: /**
   * @file HoughLines.java
   * @brief This program demonstrates line finding with the Hough transform
   */
  
  import org.opencv.core.*;
  import org.opencv.core.Point;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  import org.opencv.imgproc.Imgproc;
  
  class HoughLinesRun {
  
      public void run(String[] args) {
          // Declare the output variables
          Mat dst = new Mat(), cdst = new Mat(), cdstP;
  
          //! [load]
          String default_file = "../../../../data/sudoku.png";
          String filename = ((args.length > 0) ? args[0] : default_file);
  
          // Load an image
          Mat src = Imgcodecs.imread(filename, Imgcodecs.IMREAD_GRAYSCALE);
  
          // Check if image is loaded fine
          if( src.empty() ) {
              System.out.println("Error opening image!");
              System.out.println("Program Arguments: [image_name -- default "
                      + default_file +"] \n");
              System.exit(-1);
          }
          //! [load]
  
          //! [edge_detection]
          // Edge detection
          Imgproc.Canny(src, dst, 50, 200, 3, false);
          //! [edge_detection]
  
          // Copy edges to the images that will display the results in BGR
          Imgproc.cvtColor(dst, cdst, Imgproc.COLOR_GRAY2BGR);
          cdstP = cdst.clone();
  
          //! [hough_lines]
          // Standard Hough Line Transform
          Mat lines = new Mat(); // will hold the results of the detection
          Imgproc.HoughLines(dst, lines, 1, Math.PI/180, 150); // runs the actual detection
          //! [hough_lines]
          //! [draw_lines]
          // Draw the lines
          for (int x = 0; x < lines.rows(); x++) {
              double rho = lines.get(x, 0)[0],
                      theta = lines.get(x, 0)[1];
  
              double a = Math.cos(theta), b = Math.sin(theta);
              double x0 = a*rho, y0 = b*rho;
              Point pt1 = new Point(Math.round(x0 + 1000*(-b)), Math.round(y0 + 1000*(a)));
              Point pt2 = new Point(Math.round(x0 - 1000*(-b)), Math.round(y0 - 1000*(a)));
              Imgproc.line(cdst, pt1, pt2, new Scalar(0, 0, 255), 3, Imgproc.LINE_AA, 0);
          }
          //! [draw_lines]
  
          //! [hough_lines_p]
          // Probabilistic Line Transform
          Mat linesP = new Mat(); // will hold the results of the detection
          Imgproc.HoughLinesP(dst, linesP, 1, Math.PI/180, 50, 50, 10); // runs the actual detection
          //! [hough_lines_p]
          //! [draw_lines_p]
          // Draw the lines
          for (int x = 0; x < linesP.rows(); x++) {
              double[] l = linesP.get(x, 0);
              Imgproc.line(cdstP, new Point(l[0], l[1]), new Point(l[2], l[3]), new Scalar(0, 0, 255), 3, Imgproc.LINE_AA, 0);
          }
          //! [draw_lines_p]
  
          //! [imshow]
          // Show results
          HighGui.imshow("Source", src);
          HighGui.imshow("Detected Lines (in red) - Standard Hough Line Transform", cdst);
          HighGui.imshow("Detected Lines (in red) - Probabilistic Line Transform", cdstP);
          //! [imshow]
  
          //! [exit]
          // Wait and Exit
          HighGui.waitKey();
          System.exit(0);
          //! [exit]
      }
  }
  
  public class HoughLines {
      public static void main(String[] args) {
          // Load the native library.
          System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
          new HoughLinesRun().run(args);
      }
  }
  