OpenCV - Reading an Image as Grayscale


The following program demonstrates how to read a colored image as grayscale and display it using JavaFX window. In here, we have read the image by passing the flag IMREAD_GRAYSCALE along with the String holding the path of a colored image.

import java.awt.image.BufferedImage;

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;

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;

public class ReadingAsGrayscale extends Application {
   public void start(Stage stage) throws Exception {
      WritableImage writableImage = loadAndConvert();

      // Setting the image view
      ImageView imageView = new ImageView(writableImage);

      // Setting the position of the image

      // setting the fit height and width of the image view
      // Setting the preserve ratio of the image view
      // Creating a Group object  
      Group root = new Group(imageView);
      // Creating a scene object
      Scene scene = new Scene(root, 600, 400);
      // Setting title to the Stage
      stage.setTitle("Reading image as grayscale");
      // Adding scene to the stage
      // Displaying the contents of the stage;
   public WritableImage loadAndConvert() throws Exception {
      // Loading the OpenCV core library
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );

      // Instantiating the imagecodecs class
      Imgcodecs imageCodecs = new Imgcodecs();

      String input = "C:/EXAMPLES/OpenCV/sample.jpg";

      // Reading the image
      Mat src = imageCodecs.imread(input, Imgcodecs.IMREAD_GRAYSCALE);
      byte[] data1 = new byte[src.rows() * src.cols() * (int)(src.elemSize())];
      src.get(0, 0, data1);
      // Creating the buffered image
      BufferedImage bufImage = new BufferedImage(src.cols(),src.rows(), 
      // Setting the data elements to the image
      bufImage.getRaster().setDataElements(0, 0, src.cols(), src.rows(), data1);
      // Creating a WritableImage
      WritableImage writableImage = SwingFXUtils.toFXImage(bufImage, null);
      System.out.println("Image Read");
      return writableImage;
   public static void main(String args[]) throws Exception { 

Input Image

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

Sample Image

Output Image

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

GrayScale Output Image