title: how to find largest contour in java opencv
body: <p>I have used find contours and boundingrect and display it at my project. then I want to find the largest contours and display it. Is this possible? I am newbie to OpenCV java lang.</p>
  
  <p>heres my code so far:</p>
  
  <pre><code>@Override
  public void onCameraViewStarted(int width, int height) {
      mRgba = new Mat(height, width, CvType.CV_8UC4);
      mHsv = new Mat(height,width,CvType.CV_8UC3);
      hierarchy = new Mat();
      mHsvMask = new Mat();
      mDilated = new Mat();
      mEroded = new Mat();
  }
  
  @Override
  public void onCameraViewStopped() {
      mRgba.release();
      mHsv.release();
      mHsvMask.release();
      mDilated.release();
      hierarchy.release();
  
  }
  
  @Override
  public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
  
      mRgba =inputFrame.rgba();
      contours = new ArrayList&lt;MatOfPoint&gt;();
      hierarchy =new Mat();
      mHsv = new Mat();
      mHsvMask =new Mat();
  
      Imgproc.cvtColor(mRgba, mHsv, Imgproc.COLOR_RGB2HSV);
  
      Scalar lowerThreshold = new Scalar ( 0, 0, 0 ); // Blue color – lower hsv values
      Scalar upperThreshold = new Scalar ( 179, 255, 10 ); // Blue color – higher hsv values
      Core.inRange ( mHsv, lowerThreshold , upperThreshold, mHsvMask );
  
       //just some filter
     //Imgproc.dilate ( mHsvMask, mDilated, new Mat() );
      //Imgproc.erode(mDilated,mEroded,new Mat());
  
  
      Imgproc.findContours(mHsvMask, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);
  
      for ( int contourIdx=0; contourIdx &lt; contours.size(); contourIdx++ )
      {
          //Minimun size allowed for consideration
          MatOfPoint2f approxCurve = new MatOfPoint2f();
          MatOfPoint2f contour2f = new MatOfPoint2f(contours.get(contourIdx).toArray());
  
        //Processing on mMOP2f1 which is in type MatOfPoint2f
          double approxDistance = Imgproc.arcLength(contour2f,true)*0.02;
          Imgproc.approxPolyDP(contour2f,approxCurve,approxDistance,true);
  
          //convert to MatofPoint
          MatOfPoint point = new MatOfPoint(approxCurve.toArray());
  
          //get boundingrect from contour
          Rect rect = Imgproc.boundingRect(point);
  
          Imgproc.rectangle(mRgba,new Point(rect.x, rect.y), new Point(rect.x + rect.width, rect.y + rect.height), new Scalar(255, 0, 0, 255),3);
          //bisa Imgproc.rectangle(mRgba, rect.tl(), rect.br(), new Scalar(255, 0, 0),1, 8,0);
  
  
          //show contour kontur
          if(Imgproc.contourArea(contours.get(contourIdx))&gt;100) {
              Imgproc.drawContours(mRgba, contours, contourIdx, new Scalar(0,255,0), 5);
          }
      }
      return mRgba;
  </code></pre>
  
  <p>Hopefully, someone has some experience in this. Thanks..</p>