Creating an off-screen image
Drawing into the image
Saving the image as a JPG file

1. Create a new project in Eclipse called OffScreenImageDemo.
2. Add a new class to the project called OffScreenImageDemo.java.
3. Copy all of the code below and paste it into OffScreenImageDemo.java replacing all code that Eclipse created.
4. Create a new folder in the OffScreenImageDemo and call it Images.
5. Copy into this folder any JPG image. It is recommended that the size of the image be approximately 250 x 400 pixels.
6. Look for the place in the code below where the image Duke.jpg is being loaded and substitute the name of your image.
7. Save - Compile - Run. Study the comments and study the grahics object at the Java API website (link is found on the previous page).

package pkgOffScreenImageDemo;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.Calendar;

import javax.imageio.ImageIO;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.BevelBorder;

//================================================================
/** This application demonstrates how to create an off screen
 *  image, draw on the image, then save it as a .jpg file.
 *  @author Dr. Rick Coleman
 *  date: February 2009
 */
//================================================================
public class OffScreenImageDemo extends JFrame
{
	/** Main panel with the widgets */
	private JPanel m_MainPanel;
	
	/** The buffered image we draw into */
	private BufferedImage m_OffScreenImg;
	
	/** Label */
	private JLabel m_DoneLabel;
	
	/** Exit button */
	private JButton m_ExitButton;
	
	/** Reference to the image to draw offscreen */
	private Image m_Image;

	/** Defined width for the image */
	public static final int IMG_WIDTH = 1600;
	
	/** Defined height for the image */
	public static final int IMG_HEIGHT = 900;
	
	/** A really big font for a large image */ 
	public static final Font SysFont20B = new Font("SansSerif", Font.BOLD, 20);

	//----------------------------------------------------
	/** Default constructor */
	//----------------------------------------------------
	public OffScreenImageDemo()
	{
		// A small dialog box will appear on screen when the off-screen drawing
		// is complete and the JPG image has been created in the project folder. 
		this.setSize(320, 240);
		this.setLocation(100, 100);
		this.setTitle("Creating JPG files from Offscreen images");
		this.setDefaultCloseOperation(EXIT_ON_CLOSE);
		
		m_MainPanel = new JPanel();
		m_MainPanel.setLayout(null);
		m_MainPanel.setBackground(Color.LIGHT_GRAY);
		this.getContentPane().add(m_MainPanel);

		m_DoneLabel = new JLabel("Image file is done.");
		m_DoneLabel.setSize(300, 30);
		m_DoneLabel.setLocation(70, 50);
		m_DoneLabel.setFont(this.SysFont20B);
		m_MainPanel.add(m_DoneLabel);
		
		// Create the exit button
		m_ExitButton = new JButton("Exit");
		m_ExitButton.setSize(75, 20);
		m_ExitButton.setLocation(115, 150);
		m_ExitButton.setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED));
		m_ExitButton.addActionListener(
				new ActionListener()
				{
					public void actionPerformed(ActionEvent e)
					{
						// Exit the application with status=0 (normal exit)
						System.exit(0);
					}
				});
		m_MainPanel.add(m_ExitButton);

		// Load an image to draw on the offscreen image
		Toolkit tk = Toolkit.getDefaultToolkit();
		m_Image = tk.createImage("./Images/Duke.jpg"); // SUBSTITUTE THE NAME OF YOUR IMAGE HERE
		while(m_Image.getWidth(this) < 0); // Wait for all of the image to load

		// Create the buffered image
		m_OffScreenImg = new BufferedImage(IMG_WIDTH, IMG_HEIGHT, BufferedImage.TYPE_INT_RGB);
		
		// Draw some stuff in the buffered image
		drawSomeStuff();
		// Save the image as a JPG file
		saveJPGImage();
		
		this.setVisible(true);
	}
	
	//----------------------------------------------------
	/** drawSomeStuff - Draw into the offscreen image */
	//----------------------------------------------------
	private void drawSomeStuff()
	{
		Graphics g = m_OffScreenImg.getGraphics();
		
		// Create a white background
		g.setColor(Color.WHITE);
		g.fillRect(0, 0, m_OffScreenImg.getWidth(), m_OffScreenImg.getHeight());
		
		// Draw 3 filled squares
		g.setColor(Color.RED);
		g.fillRect(25, 25, 100, 100);
		g.setColor(Color.GREEN);
		g.fillRect(125, 125, 100, 100);
		g.setColor(Color.BLUE);
		g.fillRect(225, 225, 100, 100);
		g.setColor(Color.BLACK);
		g.setFont(SysFont20B);
		g.drawString("Filled Rectangles", 125, 350);
		
		// Draw 3 filled circles
		g.setColor(Color.RED);
		g.fillOval(325, 25, 100, 100);
		g.setColor(Color.GREEN);
		g.fillOval(425, 125, 100, 100);
		g.setColor(Color.BLUE);
		g.fillOval(525, 225, 100, 100);
		g.setColor(Color.BLACK);
		g.drawString("Filled Ovals", 425, 350);

		// Draw 3 filled rounded rectangles
		g.setColor(Color.RED);
		g.fillRoundRect(625, 25, 100, 100, 20, 20);
		g.setColor(Color.GREEN);
		g.fillRoundRect(725, 125, 100, 100, 20, 20);
		g.setColor(Color.BLUE);
		g.fillRoundRect(825, 225, 100, 100, 20, 20);
		g.setColor(Color.BLACK);
		g.drawString("Filled Rounded Rectangles", 725, 350);
		
		// Draw 3 filled arcs
		g.setColor(Color.RED);
		g.fillArc(925, 25, 100, 100, 0, 120);
		g.setColor(Color.GREEN);
		g.fillArc(1025, 125, 100, 100, 120, 120);
		g.setColor(Color.BLUE);
		g.fillArc(1125, 225, 100, 100, 240, 120);
		g.setColor(Color.BLACK);
		g.drawString("Filled Arcs", 1025, 350);
	
		// Draw 3 squares
		g.setColor(Color.RED);
		g.drawRect(25, 425, 100, 100);
		g.setColor(Color.GREEN);
		g.drawRect(125, 525, 100, 100);
		g.setColor(Color.BLUE);
		g.drawRect(225, 625, 100, 100);
		g.setColor(Color.BLACK);
		g.setFont(SysFont20B);
		g.drawString("Rectangles", 125, 750);
		
		// Draw 3 circles
		g.setColor(Color.RED);
		g.drawOval(325, 425, 100, 100);
		g.setColor(Color.GREEN);
		g.drawOval(425, 525, 100, 100);
		g.setColor(Color.BLUE);
		g.drawOval(525, 625, 100, 100);
		g.setColor(Color.BLACK);
		g.drawString("Ovals", 425, 750);

		// Draw 3 rounded rectangles
		g.setColor(Color.RED);
		g.drawRoundRect(625, 425, 100, 100, 20, 20);
		g.setColor(Color.GREEN);
		g.drawRoundRect(725, 525, 100, 100, 20, 20);
		g.setColor(Color.BLUE);
		g.drawRoundRect(825, 625, 100, 100, 20, 20);
		g.setColor(Color.BLACK);
		g.drawString("Rounded Rectangles", 725, 750);
		
		// Draw 3 arcs
		g.setColor(Color.RED);
		g.drawArc(925, 425, 100, 100, 0, 120);
		g.setColor(Color.GREEN);
		g.drawArc(1025, 525, 100, 100, 120, 120);
		g.setColor(Color.BLUE);
		g.drawArc(1125, 625, 100, 100, 240, 120);
		g.setColor(Color.BLACK);
		g.drawString("Arcs", 1025, 750);
	
		// Draw the Image
		g.drawImage(m_Image, 1250, 200, null);
		g.drawString("Duke, the Java Mascot", 1255, 650);
	}

	//----------------------------------------------------
	/** saveJPGImage - Save the image as a JPG file */
	//----------------------------------------------------
	private void saveJPGImage()
	{
		File imgFile;

		// Create a unique name using the time
		// Note: Calendar months are numbered from 0 so add 1 to Calendar.MONTH
		Calendar cd = Calendar.getInstance();
		int hr = cd.get(Calendar.HOUR_OF_DAY);
		int min = cd.get(Calendar.MINUTE);
		int sec = cd.get(Calendar.SECOND);
		int day = cd.get(Calendar.DAY_OF_MONTH);
		int month = cd.get(Calendar.MONTH)+1; // Calendar months are numbered from 0 
		int year = cd.get(Calendar.YEAR);

		// Create an image file name
		String fileName = new String("Image_" 
                + ((hr<10)?("0"+String.valueOf(hr)):String.valueOf(hr)) 
                + ((min<10)?("0"+String.valueOf(min)):String.valueOf(min))
                + ((sec<10)?("0"+String.valueOf(sec)):String.valueOf(sec)) 
                + "_" + ((day<10)?("0"+String.valueOf(day)):String.valueOf(day))
                + ((month<10)?("0"+String.valueOf(month)):String.valueOf(month))
                + year + ".jpg");
		// Create an image file
		imgFile = new File(fileName);
		// Save the image in JPEG format
		try
		{
			ImageIO.write(m_OffScreenImg, "jpg", imgFile);
		}
		catch(Exception e)
		{
			System.out.println("Failed to write image to disk.");
		}

	}
	
	//----------------------------------------------------
	/** main function */
	//----------------------------------------------------
	public static void main(String[] args)
	{
		OffScreenImageDemo demo = new OffScreenImageDemo();
	}
}