Apply Opening Operation to an Image using OpenCV

Opening is a morphological image processing operation when erosion operation is applied to an image and then dilation operation. Opening operation allows removing small objects while preserving the size of larger objects.

The morphologyEx function with MORPH_OPEN parameter can be used to apply the opening operation to an image.

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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.morphologyEx(inputImg, cv2.MORPH_OPEN, kernel)

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

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#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;
    morphologyEx(inputImg, outputImg, MORPH_OPEN, kernel);

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

    return 0;
}

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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.morphologyEx(inputImg, outputImg, Imgproc.MORPH_OPEN, kernel);

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

        System.exit(0);
    }
}