ImageToByteArray.java

import java.nio.ByteBuffer;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.PixelReader;
import javafx.scene.image.WritablePixelFormat;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Line;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class ImageToByteArray extends Application {

	@Override
	public void start(Stage primaryStage) {
		Rectangle rect = new Rectangle(200, 80, Color.NAVY);
		Line upDiag = new Line(0, 80, 200, 0);
		upDiag.setStroke(Color.WHITE);
		upDiag.setStrokeWidth(10);
		
		Line downDiag = new Line(0, 0, 200, 80);
		downDiag.setStroke(Color.WHITE);
		downDiag.setStrokeWidth(10);
		
		Pane flag = new Pane(rect, upDiag, downDiag);
		
		Scene scene = new Scene(flag, 200, 80);
		primaryStage.setScene(scene);
		primaryStage.show();
		
		Image img = flag.snapshot(null, null);
		
	    PixelReader pr = img.getPixelReader();

	    WritablePixelFormat<ByteBuffer> pixelformat = WritablePixelFormat.getByteBgraInstance();

	    int w = (int) img.getWidth();
	    int h = (int) img.getHeight();
	    int offset = 0;
	    int scanlineStride = w * 4;

	    byte[] buffer = new byte[w * h * 4];

	    pr.getPixels(0, 0, w, h, pixelformat, buffer, offset, scanlineStride);
	    
	    // portion near the center:
	    for (int i = 30780; i < 30880; i++) System.out.println(Byte.toUnsignedInt(buffer[i]));

	}

	public static void main(String[] args) {
		launch(args);
	}
}