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Altering the brightness and contrast of an image using JavaFX and OpenCV
The convertTo() method of the org.opencv.core.Mat class accepts 4 parameters namely: mat(empty matrix), rtype(integer), alpha(integer), beta(integer), in the same order.
To increase the brightness − You need to reduce the beta value from 0 towards -255(keeping alpha value 1).
To decrease the brightness − You need to increase the beta value from 0 towards 255(keeping alpha value 1).
To increase the contrast − You need to increase the alpha value from 1 towards 100(keeping beta value 0).
To decrease the contrast − You need to decrease the alpha value from 1 to 0 (keeping beta value 0).
Example
Following is a JavaFX program with two slide bars to alter the alpha beta values.
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.embed.swing.SwingFXUtils;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Slider;
import javafx.scene.image.ImageView;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javax.imageio.ImageIO;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.MatOfByte;
import org.opencv.imgcodecs.Imgcodecs;
public class AlphaBetaValuesJavaFX extends Application {
double contrast = 1;
private final int rtype = -1;
double alpha = 1;
double beta = 0;
Slider slider1;
Slider slider2;
Mat src = null;
public void start(Stage stage) throws IOException {
//Loading the OpenCV core library
System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
String file ="D:\Image\lamma2.jpg";
src = Imgcodecs.imread(file);
WritableImage writableImage = loadImage(src);
//Setting the image view
ImageView imageView = new ImageView(writableImage);
imageView.setX(50);
imageView.setY(25);
imageView.setFitHeight(400);
imageView.setFitWidth(550);
imageView.setPreserveRatio(true);
Label label1 = new Label("Alpha value");
//Setting the slider
slider1 = new Slider(0.1, 3, 1);
slider1.setShowTickLabels(true);
slider1.setShowTickMarks(true);
slider1.setMajorTickUnit(1);
slider1.setBlockIncrement(0.05);
//Setting the label
Label label2 = new Label();
Label label3 = new Label("Beta value");
//Setting the slider
slider2 = new Slider(-100, 100, 0);
slider2.setShowTickLabels(true);
slider2.setShowTickMarks(true);
slider2.setMajorTickUnit(25);
slider2.setBlockIncrement(10);
//Setting the label
Label label4 = new Label();
//Listener for the slider
slider1.valueProperty().addListener(new ChangeListener<Number>() {
public void changed(ObservableValue <?extends Number>observable, Number oldValue, Number newValue){
try {
label2.setText("α-value: " + newValue);
alpha = newValue.doubleValue();
Mat dest = new Mat(src.rows(), src.cols(), src.type());
src.convertTo(dest, rtype, alpha, beta);
imageView.setImage(loadImage(dest));
}
catch(Exception e) {
System.out.println("");
}
}
});
slider2.valueProperty().addListener(new ChangeListener<Number>() {
public void changed(ObservableValue <?extends Number>observable, Number oldValue, Number newValue){
try {
label4.setText("β-value: " + newValue);
beta = newValue.doubleValue();
Mat dest = new Mat(src.rows(), src.cols(), src.type());
src.convertTo(dest, rtype, alpha, beta);
imageView.setImage(loadImage(dest));
}
catch(Exception e) {
System.out.println("");
}
}
});
//VBox to arrange all the three components
VBox vbox = new VBox();
vbox.setPadding(new Insets(20));
vbox.setSpacing(10);
vbox.getChildren().addAll(label1, slider1, label2, imageView, label3, slider2, label4);
//Creating a scene object
Scene scene = new Scene(vbox, 600, 580);
stage.setTitle("Loading an image");
stage.setScene(scene);
stage.show();
}
public WritableImage loadImage(Mat image) throws IOException {
MatOfByte matOfByte = new MatOfByte();
Imgcodecs.imencode(".jpg", image, matOfByte);
//Storing the encoded Mat in a byte array
byte[] byteArray = matOfByte.toArray();
//Displaying the image
InputStream in = new ByteArrayInputStream(byteArray);
BufferedImage bufImage = ImageIO.read(in);
System.out.println("Image Loaded");
WritableImage writableImage = SwingFXUtils.toFXImage(bufImage, null);
return writableImage;
}
public static void main(String args[]) {
launch(args);
}
}Input image
Output
Updated on: 09-Apr-2020
442 Views
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