How to draw polylines in OpenCV using Java?

The org.opencv.imgproc package of Java OpenCV library contains a class named Imgproc this class provides various methods to process an input image such as resize(), filter2D, etc.. In addition to these It also provides a set of method to draw geometrical shapes on images.

Among them to draw a polylines you need to invoke the polylines() method of this class. This method accepts the following parameters −

  • A Mat object representing the image on which the polygon is to be drawn.

  • A-List object holding the objects of the type MatOfPoint.

  • A parameter of the type boolean specifying whether the poly-lines are closed.

  • A Scalar object representing the color of the polygon.

  • An integer representing the thickness of the polygon(default:1).


import java.util.ArrayList;
import java.util.List;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.MatOfPoint;
import org.opencv.core.Point;
import org.opencv.core.Scalar;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
public class DrawingPolyines {
   Mat matrix = null;
   public static void main(String args[]) {
      //Loading the OpenCV core library
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
      //Loading the OpenCV core library
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
      //Reading the source image in to a Mat object
      Mat src = Imgcodecs.imread("D:\images\blank.jpg");
      //Drawing an polygon
      List<MatOfPoint> list = new ArrayList<MatOfPoint>();
      list.add( new MatOfPoint (
         new Point(208, 71), new Point(421, 161),
         new Point(226, 232), new Point(332, 52),
         new Point(363, 250)));
      boolean isClosed = true;
      Scalar color = new Scalar(64, 64, 64);
      int thickness = 10;
      Imgproc.polylines (src, list, isClosed, color, thickness);
      //Saving and displaying the image
      Imgcodecs.imwrite("arrowed_line.jpg", src);
      HighGui.imshow("Drawing a polylines", src);


On executing, the above program generates the following window −

Updated on: 10-Apr-2020


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