Question

In this part of the Java 2D tutorial, we will work with images.

BufferedImage is a fundamental class for working with images in Java 2D. It is a rectangle of pixels stored in memory.

Displaying an Image

In the first example, we display an image on the panel.

DisplayImageEx.java

package com.zetcode;

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;

class Surface extends JPanel {

  private Image mshi;

  public Surface() {
    
    loadImage();
    setSurfaceSize();
  }

  private void loadImage() {

    mshi = new ImageIcon("mushrooms.jpg").getImage();
  }
  
  private void setSurfaceSize() {
    
    Dimension d = new Dimension();
    d.width = mshi.getWidth(null);
    d.height = mshi.getHeight(null);
    setPreferredSize(d);    
  }

  private void doDrawing(Graphics g) {

    Graphics2D g2d = (Graphics2D) g;
    g2d.drawImage(mshi, 0, 0, null);
  }

  @Override
  public void paintComponent(Graphics g) {

    super.paintComponent(g);
    doDrawing(g);
  }
}

public class DisplayImageEx extends JFrame {

  public DisplayImageEx() {

    initUI();
  }

  private void initUI() {

    add(new Surface());

    pack();
    
    setTitle("Mushrooms");
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  public static void main(String[] args) {

    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run() {
        DisplayImageEx ex = new DisplayImageEx();
        ex.setVisible(true);
      }
    });
  }
}

In the example, we display an image on the panel. The window is resized to fit the size of the image.

private void loadImage() {

  mshi = new ImageIcon("mushrooms.jpg").getImage();
}

We use the ImageIcon class to load the image. The image is located in the current working directory.

private void setSurfaceSize() {
  
  Dimension d = new Dimension();
  d.width = mshi.getWidth(null);
  d.height = mshi.getHeight(null);
  setPreferredSize(d);    
}

We determine the size of the loaded image. With the setPreferredSize() method, we set the preferred size of the Surface panel. The pack() method of the JFrame container will cause the frame to fit the size of its children. In our case the Surface panel. As a consequence, the window will be sized to exactly display the loaded image.

private void doDrawing(Graphics g) {

  Graphics2D g2d = (Graphics2D) g;
  g2d.drawImage(mshi, 0, 0, null);
}

The image is drawn on the panel using the drawImage() method. The last parameter is the ImageObserver class. It is sometimes used for asynchronous loading. When we do not need asynchronous loading of our images, we can just put null there.

private void initUI() {
  ...
  pack();
  ...
}

The pack() method sizes the container to fit the size of the child panel.

Grayscale image

In computing, a grayscale digital image is an image in which the value of each pixel is a single sample, that is, it carries the full (and only) information about its intensity. Images of this sort are composed exclusively of shades of neutral gray, varying from black at the weakest intensity to white at the strongest. (Wikipedia)

In the next example, we create a grayscale image with Java 2D.

GrayScaleImage.java

package com.zetcode;

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;

class Surface extends JPanel {

  private Image mshi;
  private BufferedImage bufimg;
  private Dimension d;

  public Surface() {

    loadImage();
    determineAndSetSize();
    createGrayImage();
  }

  private void determineAndSetSize() {

    d = new Dimension();
    d.width = mshi.getWidth(null);
    d.height = mshi.getHeight(null);
    setPreferredSize(d);
  }
  
  private void createGrayImage() {
    
    bufimg = new BufferedImage(d.width, d.height, 
        BufferedImage.TYPE_BYTE_GRAY);

    Graphics2D g2d = bufimg.createGraphics();
    g2d.drawImage(mshi, 0, 0, null);
    g2d.dispose();    
  }

  private void loadImage() {

    mshi = new ImageIcon("mushrooms.jpg").getImage();
  }

  private void doDrawing(Graphics g) {

    Graphics2D g2d = (Graphics2D) g;
    g2d.drawImage(bufimg, null, 0, 0);
  }

  @Override
  public void paintComponent(Graphics g) {

    super.paintComponent(g);
    doDrawing(g);
  }
}

public class GrayScaleImageEx extends JFrame {

  public GrayScaleImageEx() {
    
    initUI();
  }

  private void initUI() {

    Surface dpnl = new Surface();
    add(dpnl);

    pack();
    
    setTitle("GrayScale image");
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  public static void main(String[] args) {

    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run() {
        GrayScaleImageEx ex = new GrayScaleImageEx();
        ex.setVisible(true);
      }
    });
  }
}

There are several ways to create a grayscale image. We do it by writing image data into buffered image of BufferedImage.TYPE_BYTE_GRAY type.

bufimg = new BufferedImage(d.width, d.height, 
    BufferedImage.TYPE_BYTE_GRAY);

We create a BufferedImage class of type BufferedImage.TYPE_BYTE_GRAY .

Graphics2D g2d = bufimg.createGraphics();
g2d.drawImage(mshi, 0, 0, null);

Here we draw the mushrooms image into the buffered image.

g2d.dispose();    

Graphics objects created with createGraphics() method should be manually released. Graphics objects which are provided as arguments to the paint() and update() methods of components are automatically released by the system when those methods return.

private void doDrawing(Graphics g) {

  Graphics2D g2d = (Graphics2D) g;
  g2d.drawImage(bufimg, null, 0, 0);
}

The buffered image is drawn on the panel with the drawImage() method.

Flipped image

The following example flips image. We are going to filter the image. There is a filter() method which is transforming images.

FlippedImageEx.java

package com.zetcode;

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.geom.AffineTransform;
import java.awt.image.AffineTransformOp;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;

class Surface extends JPanel {

  private Image mshi;
  private BufferedImage bufimg;
  private final int SPACE = 10;

  public Surface() {

    loadImage();
    createFlippedImage();
    setSurfaceSize();
  }

  private void loadImage() {

    mshi = new ImageIcon("mushrooms.jpg").getImage();
  }

  private void createFlippedImage() {
    
    bufimg = new BufferedImage(mshi.getWidth(null),
        mshi.getHeight(null), BufferedImage.TYPE_INT_RGB);
    
    Graphics gb = bufimg.getGraphics();
    gb.drawImage(mshi, 0, 0, null);
    gb.dispose();

    AffineTransform tx = AffineTransform.getScaleInstance(-1, 1);
    tx.translate(-mshi.getWidth(null), 0);
    AffineTransformOp op = new AffineTransformOp(tx,
        AffineTransformOp.TYPE_NEAREST_NEIGHBOR);
    bufimg = op.filter(bufimg, null);    
  }
  
  private void setSurfaceSize() {
        
    int w = bufimg.getWidth();
    int h = bufimg.getHeight();
    
    Dimension d = new Dimension(3*SPACE+2*w, h+2*SPACE);
    setPreferredSize(d);
  }

  private void doDrawing(Graphics g) {

    Graphics2D g2d = (Graphics2D) g;

    g2d.drawImage(mshi, SPACE, SPACE, null);
    g2d.drawImage(bufimg, null, 2*SPACE + bufimg.getWidth(), SPACE);
  }

  @Override
  public void paintComponent(Graphics g) {

    super.paintComponent(g);
    doDrawing(g);
  }
}

public class FlippedImageEx extends JFrame {

  public FlippedImageEx() {

    initUI();
  }

  private void initUI() {

    add(new Surface());
    pack();

    setTitle("Flipped image");
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  public static void main(String[] args) {

    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run() {
        FlippedImageEx ex = new FlippedImageEx();
        ex.setVisible(true);
      }
    });
  }
}

In our code example, we horizontally flip an image.

AffineTransform tx = AffineTransform.getScaleInstance(-1, 1);
tx.translate(-castle.getWidth(null), 0);

Flipping an image means scaling it and translating it. So we do an AffineTransform operation.

AffineTransformOp op = new AffineTransformOp(tx, 
            AffineTransformOp.TYPE_NEAREST_NEIGHBOR);
bufferedImage = op.filter(bufferedImage, null)

This is one of the filtering operations available. This could be also done by pixel manipulation. But Java 2D provides high level classes that make it easier to manipulate images. In our case, the AffineTransformOp class performs scaling and translation on the image pixels.

private void doDrawing(Graphics g) {

  Graphics2D g2d = (Graphics2D) g;

  g2d.drawImage(mshi, SPACE, SPACE, null);
  g2d.drawImage(bufimg, null, 2*SPACE + bufimg.getWidth(), SPACE);
}

Both images are painted on the panel.

private void setSurfaceSize() {
      
  int w = bufimg.getWidth();
  int h = bufimg.getHeight();
  
  Dimension d = new Dimension(3*SPACE+2*w, h+2*SPACE);
  setPreferredSize(d);
}

We set the preferred size for the panel. We calculate the size so that we can place two images on the panel and put some space between them, and the images and the window borders.

Blurred image

The next code example blurs an image. A blur means an unfocused image. To blur an image, we use a convolution operation. It is a mathematical operation which is also used in edge detection or noise elimination. Blur operations can be used in various graphical effects. For example creating speed illusion or showing an unfocused vision of a human.

The blur filter operation replaces each pixel in image with an average of the pixel and its neighbours. Convolutions are per-pixel operations. The same arithmetic is repeated for every pixel in the image. A kernel can be thought of as a two-dimensional grid of numbers that passes over each pixel of an image in sequence, performing calculations along the way. Since images can also be thought of as two-dimensional grids of numbers, applying a kernel to an image can be visualized as a small grid (the kernel) moving across a substantially larger grid (the image). (developer.apple.com)

BlurredImageEx.java

package com.zetcode;

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.image.BufferedImageOp;
import java.awt.image.ConvolveOp;
import java.awt.image.Kernel;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

class Surface extends JPanel {

  private BufferedImage mshi;
  private BufferedImage bluri;

  public Surface() {

    loadImage();
    createBlurredImage();
    setSurfaceSize();
  }

  private void loadImage() {
    
    try {
      
      mshi = ImageIO.read(new File("mushrooms.jpg"));
    } catch (IOException ex) {
      
      Logger.getLogger(Surface.class.getName()).log(
          Level.WARNING, null, ex);
    }
  }
  
  private void createBlurredImage() {

    float[] blurKernel = {
      1 / 9f, 1 / 9f, 1 / 9f,
      1 / 9f, 1 / 9f, 1 / 9f,
      1 / 9f, 1 / 9f, 1 / 9f
    };

    BufferedImageOp blur = new ConvolveOp(new Kernel(3, 3, blurKernel));
    bluri = blur.filter(mshi, new BufferedImage(mshi.getWidth(),
        mshi.getHeight(), mshi.getType()));
  }
  
  private void setSurfaceSize() {
    
    Dimension d = new Dimension();
    d.width = mshi.getWidth(null);
    d.height = mshi.getHeight(null);
    setPreferredSize(d);    
  }

  private void doDrawing(Graphics g) {

    Graphics2D g2d = (Graphics2D) g;
    g2d.drawImage(bluri, null, 0, 0);
  }

  @Override
  public void paintComponent(Graphics g) {

    super.paintComponent(g);
    doDrawing(g);
  }
}

public class BlurredImageEx extends JFrame {

  public BlurredImageEx() {

    setTitle("Blurred image");
    add(new Surface());

    pack();
    
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  public static void main(String[] args) {

    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run() {
        
        BlurredImageEx ex = new BlurredImageEx();
        ex.setVisible(true);
      }
    });
  }
}

In the code example, we load an image from the disk, perform a blur operation on the image, and display the result on the window.

private void loadImage() {
  
  try {
    
    mshi = ImageIO.read(new File("mushrooms.jpg"));
  } catch (IOException ex) {
    
    Logger.getLogger(Surface.class.getName()).log(
        Level.WARNING, null, ex);
  }
}

The the read() method of the ImageIO class reads an image from the disk and returns a BufferedImage .

float[] blurKernel = {
  1 / 9f, 1 / 9f, 1 / 9f,
  1 / 9f, 1 / 9f, 1 / 9f,
  1 / 9f, 1 / 9f, 1 / 9f
};

This matrix is called a kernel. The values are weights that are applied to the neighbouring values of the pixel being changed.

BufferedImageOp blur = new ConvolveOp(new Kernel(3, 3, blurKernel));
bluri = blur.filter(mshi, new BufferedImage(mshi.getWidth(),
    mshi.getHeight(), mshi.getType()));

Here we apply the blur filter on the image.

private void doDrawing(Graphics g) {

  Graphics2D g2d = (Graphics2D) g;
  g2d.drawImage(bluri, null, 0, 0);
}

The blurred image is drawn on the window.

Reflection

In the next example we show a reflected image. This effect makes an illusion as if the image was reflected in water. The following code example was inspired by the code from jhlabs.com .

ReflectionEx.java

package com.zetcode;

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;

class Surface extends JPanel {

  private BufferedImage image;
  private BufferedImage refImage;
  private int img_w;
  private int img_h;
  private final int SPACE = 30;

  public Surface() {

    loadImage();
    getImageSize();
    createReflectedImage();
  }

  private void loadImage() {

    try {

      image = ImageIO.read(new File("rotunda.jpg"));
    } catch (Exception ex) {

      Logger.getLogger(Surface.class.getName()).log(
          Level.WARNING, null, ex);
    }
  }

  private void getImageSize() {

    img_w = image.getWidth();
    img_h = image.getHeight();
  }

  private void createReflectedImage() {
    
    float opacity = 0.4f;
    float fadeHeight = 0.3f;
    
    refImage = new BufferedImage(img_w, img_h,
        BufferedImage.TYPE_INT_ARGB);    
    Graphics2D rg = refImage.createGraphics();
    rg.drawImage(image, 0, 0, null);
    rg.setComposite(AlphaComposite.getInstance(AlphaComposite.DST_IN));
    rg.setPaint(new GradientPaint(0, img_h * fadeHeight,
        new Color(0.0f, 0.0f, 0.0f, 0.0f), 0, img_h,
        new Color(0.0f, 0.0f, 0.0f, opacity)));

    rg.fillRect(0, 0, img_w, img_h);
    rg.dispose();
  }

  private void doDrawing(Graphics g) {

    Graphics2D g2d = (Graphics2D) g.create();

    int win_w = getWidth();
    int win_h = getHeight();

    int gap = 20;

    g2d.setPaint(new GradientPaint(0, 0, Color.black, 0, 
        win_h, Color.darkGray));
    g2d.fillRect(0, 0, win_w, win_h);
    g2d.translate((win_w - img_w) / 2, win_h / 2 - img_h);
    g2d.drawImage(image, 0, 0, null);
    g2d.translate(0, 2 * img_h + gap);
    g2d.scale(1, -1);

    g2d.drawImage(refImage, 0, 0, null);
    
    g2d.dispose();
  }

  @Override
  public void paintComponent(Graphics g) {

    super.paintComponent(g);
    doDrawing(g);
  }

  @Override
  public Dimension getPreferredSize() {

    return new Dimension(img_w + 2 * SPACE, 2 * img_h + 3 * SPACE);
  }
}

public class ReflectionEx extends JFrame {

  public ReflectionEx() {

    initUI();
  }

  private void initUI() {

    add(new Surface());
    pack();
    
    setTitle("Reflection");
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

  public static void main(String[] args) {

    EventQueue.invokeLater(new Runnable() {
      @Override
      public void run() {
        
        ReflectionEx ex = new ReflectionEx();
        ex.setVisible(true);
      }
    });
  }
}

In the example, we create an illusion of a reflected image.

refImage = new BufferedImage(img_w, img_h,
    BufferedImage.TYPE_INT_ARGB);    
Graphics2D rg = refImage.createGraphics();
rg.drawImage(image, 0, 0, null);

A copy of a loaded image is created.

rg.setComposite(AlphaComposite.getInstance(AlphaComposite.DST_IN));
rg.setPaint(new GradientPaint(0, img_h * fadeHeight,
    new Color(0.0f, 0.0f, 0.0f, 0.0f), 0, img_h,
    new Color(0.0f, 0.0f, 0.0f, opacity)));

rg.fillRect(0, 0, img_w, img_h);

This is the most important part of the code. We make the second image transparent. But the transparency is not constant; the image gradually fades out. This is achieved with the GradientPaint class.

g2d.setPaint(new GradientPaint(0, 0, Color.black, 0, 
    win_h, Color.darkGray));
g2d.fillRect(0, 0, win_w, win_h);

The background of the window is filled with a gradient paint. The paint is a smooth blending from black to dark gray.

g2d.translate((win_w - img_w) / 2, win_h / 2 - img_h);
g2d.drawImage(image, 0, 0, null);

The normal image is moved to the center of the window and drawn.

g2d.translate(0, 2 * imageHeight + gap);
g2d.scale(1, -1);

This code flips the image and translates it below the original image. The translation operation is necessary because the scaling operation makes the image upside down and translates the image up. To understand what happens, simply take a photograph and place it on the table and flip it.

g2d.drawImage(refImage, 0, 0, null);

The reflected image is drawn.

@Override
public Dimension getPreferredSize() {

  return new Dimension(img_w + 2 * SPACE, 2 * img_h + 3 * SPACE);
}

Another way to set a preferred size for a component is to override the getPreferredSize() method.

Figure: Reflection

In this part of the Java2D tutorial we have worked with images.