What is morphological gradient in image processing?

Erosion and dilation are the two basic morphological operations. As the name implies, morphological operations are the set of operations that process images according to their shapes.

During dilation operation additional pixels are added to an image boundary and, during erosion operation, additional pixels are removed from image boundaries, The total number of pixels added during the dilation process depends on the dimensions of the structuring element used.

Morphological Gradient is the operation that is equal to the difference between dilation and erosion of an image. Each pixel value in the resulting image indicates the contrast intensity in the nearby pixels. This is used in edge detection, segmentation and to find the outline of an object.

Example

Following Java example generates a window containing the Morphological gradient of the given image −

import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javafx.application.Application;
import javafx.embed.swing.SwingFXUtils;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.WritableImage;
import javafx.stage.Stage;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
public class MorphologicalGradient extends Application {
   public void start(Stage stage) throws IOException {
      //Loading the OpenCV core library
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
      //Reading image data
      String file ="D:\Images\morph_input1.jpg";
      Mat src = Imgcodecs.imread(file);
      //Creating destination matrix
      Mat dst = new Mat(src.rows(), src.cols(), src.type());
      //Preparing the kernel matrix object
      Mat kernel = Mat.ones(5,5, CvType.CV_32F);
      //Applying dilate on the Image
      Imgproc.morphologyEx(src, dst, Imgproc.MORPH_GRADIENT, kernel);
      //Converting matrix to JavaFX writable image
      Image img = HighGui.toBufferedImage(dst);
      WritableImage writableImage= SwingFXUtils.toFXImage((BufferedImage) img, null);
      //Setting the image view
      ImageView imageView = new ImageView(writableImage);
      imageView.setX(10);
      imageView.setY(10);
      imageView.setFitWidth(575);
      imageView.setPreserveRatio(true);
      //Setting the Scene object
      Group root = new Group(imageView);
      Scene scene = new Scene(root, 595, 400);
      stage.setTitle("Morphological Gradient");
      stage.setScene(scene);
      stage.show();
   }
   public static void main(String args[]) {
      launch(args);
   }
}

Input Image

Output Image