Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
How to fit ellipses around possible objects in an image using OpenCV Java?
You can fit an ellipse over a shape using the fitEllipse() method of the org.opencv.imgproc.Imgproc class. This method accepts an object of MatOfPoint2f class, calculates the ellipse that would fit the given set of points and returns a RotatedRect object.
Using this you can draw ellipses around the possible objects in an image. To do so,
Read an image using the imread() method of the Imgproc class.
Convert it into a grayscale image using the cvtColor() method of the Imgproc class.
Convert the gray image to binary using the threshold() method of the Imgproc class.
Find the contours in the image using the findContours() method of the Imgproc class.
Now, get the RotatedRec objects for the possible contours bypassing each contour value as MatOfPoint2f to the fitEllipse() method.
Finally, draw ellipses around the possible shapes using the ellipse() method.
Note − To fit the ellipse the object should contain at least five points.
Example
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.MatOfPoint2f;
import org.opencv.core.RotatedRect;
import org.opencv.core.Scalar;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
public class FitEllipseExample {
public static void main(String args[]) throws Exception {
//Loading the OpenCV core library
System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
//Reading the contents of the image
String file ="D:\Images\javafx_graphical.jpg";
Mat src = Imgcodecs.imread(file);
//Converting the source image to binary
Mat gray = new Mat(src.rows(), src.cols(), src.type());
Imgproc.cvtColor(src, gray, Imgproc.COLOR_BGR2GRAY);
Mat binary = new Mat(src.rows(), src.cols(), src.type(), new Scalar(0));
Imgproc.threshold(gray, binary, 100, 255, Imgproc.THRESH_BINARY_INV);
//Finding Contours
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchey = new Mat();
Imgproc.findContours(binary, contours, hierarchey, Imgproc.RETR_TREE,
Imgproc.CHAIN_APPROX_SIMPLE);
//Empty rectangle
RotatedRect[] rec = new RotatedRect[contours.size()];
for (int i = 0; i < contours.size(); i++) {
rec[i] = new RotatedRect();
if (contours.get(i).rows() > 5) {
rec[i] = Imgproc.fitEllipse(new MatOfPoint2f(contours.get(i).toArray()));
}
Scalar color_elli = new Scalar(190, 0, 0);
Imgproc.ellipse(src, rec[i], color_elli, 5);
}
HighGui.imshow("Contours operation", src);
HighGui.waitKey();
}
}
Input Image
Output
176 Views
