Apply Dilation Operation to an Image using OpenCV

Dilation is a morphological image processing operation that increases the boundaries of the foreground object. In most case, foreground pixels are white. To apply dilation operation to an image, the kernel (structuring element) is defined. The kernel goes through the image from left-to-right and top-to-bottom. A foreground pixel in the input image will be kept if at least one pixel inside the kernel is 1. Otherwise, the pixels are set to 0. Usually, the dilation operation is used to join broken parts of an object in an image.

OpenCV provides the dilate function to apply dilation operation to an image.

import cv2
import numpy as np

inputImg = cv2.imread('test.jpg')
inputImg = cv2.cvtColor(inputImg, cv2.COLOR_BGR2GRAY)
_, inputImg = cv2.threshold(inputImg, 0, 255, cv2.THRESH_OTSU)

kernel = np.ones((4, 4))
outputImg = cv2.dilate(inputImg, kernel)

cv2.imshow('Input image', inputImg)
cv2.imshow('Output image', outputImg)
cv2.waitKey(0)
cv2.destroyAllWindows()

#include <opencv2/opencv.hpp>

using namespace cv;

int main()
{
    Mat inputImg = imread("test.jpg");
    cvtColor(inputImg, inputImg, COLOR_BGR2GRAY);
    threshold(inputImg, inputImg, 0, 255, THRESH_OTSU);

    Mat kernel = getStructuringElement(MORPH_RECT, Size(4, 4));
    Mat outputImg;
    dilate(inputImg, outputImg, kernel);

    imshow("Input image", inputImg);
    imshow("Output image", outputImg);
    waitKey(0);
    destroyAllWindows();

    return 0;
}

package app;

import org.opencv.core.*;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

public class Main
{
    static { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); }

    public static void main(String[] args)
    {
        Mat inputImg = Imgcodecs.imread("test.jpg");
        Imgproc.cvtColor(inputImg, inputImg, Imgproc.COLOR_BGR2GRAY);
        Imgproc.threshold(inputImg, inputImg, 0, 255, Imgproc.THRESH_OTSU);

        Mat kernel = Imgproc.getStructuringElement(Imgproc.MORPH_RECT, new Size(4, 4));
        Mat outputImg = new Mat();
        Imgproc.dilate(inputImg, outputImg, kernel);

        HighGui.imshow("Input image", inputImg);
        HighGui.imshow("Output image", outputImg);
        HighGui.waitKey(0);
        HighGui.destroyAllWindows();

        System.exit(0);
    }
}