The Filter2D operation convolves an image with the kernel. You can perform this operation on an image using the Filter2D() method of the imgproc class. Following is the syntax of this method −

filter2D(src, dst, ddepth, kernel)

This method accepts the following parameters −

• src − A Mat object representing the source (input image) for this operation.

• dst − A Mat object representing the destination (output image) for this operation.

• ddepth − A variable of the type integer representing the depth of the output image.

• kernel − A Mat object representing the convolution kernel.

Example

The following program demonstrates how to perform the Filter2D operation on an image.

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

public class Filter2D {
   public static void main( String[] args ) {
      //Loading the OpenCV core library  
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );

      //Reading the Image from the file and storing it in to a Matrix object
      String file ="E:/OpenCV/chap11/filter_input.jpg";
      Mat src = Imgcodecs.imread(file);

      //Creating an empty matrix to store the result
      Mat dst = new Mat();

      // Creating kernel matrix
      Mat kernel = Mat.ones(2,2, CvType.CV_32F);
      
      for(int i = 0; i<kernel.rows(); i++) {
         for(int j = 0; j<kernel.cols(); j++) {
            double[] m = kernel.get(i, j);

            for(int k = 1; k<m.length; k++) {
               m[k] = m[k]/(2 * 2);
            }
            kernel.put(i,j, m);
         }
      }
      Imgproc.filter2D(src, dst, -1, kernel);
      Imgcodecs.imwrite("E:/OpenCV/chap11/filter2d.jpg", dst);
      System.out.println("Image Processed");
   }
}

Assume that following is the input image filter_input.jpg specified in the above program.

Output

On executing the program, you will get the following output −

Image Processed

If you open the specified path, you can observe the output image as follows −