Filtering and Transforming Digital Images
In this Issue
Welcome to the Core Java Technologies Tech Tips for April 7, 2004. Here you\'ll get tips on using core Java technologies and APIs, such as those in Java 2 Platform, Standard Edition (J2SE).
Tutorial Details:
FILTERING AND TRANSFORMING DIGITAL IMAGES
The February 10, 2004 Tech Tip Styling Digital Images with ConvolveOp showed how to use java.awt.image.ConvolveOp to sharpen and blur images as well as darken and brighten images. ConvolveOp implements a convolution, which is the easiest way to blur and sharpen images. A convolution blurs images by averaging nearby pixels. It sharpens edges by highlighting differences between the colors of nearby pixels. But there are other filters and transforms you can apply to an image to meet your needs. In this tip you will apply affine transformations such as a rotation and a scale. You will also apply filters that perform linear and non-linear brightening. You will also use a color filter to transform a color image to grayscale. Each of these filters and transforms are performed by classes in the java.awt.image package that implement the interface BufferedImageOp.
As was the case in the \"Styling Digital Images with ConvolveOp\" Tech Tip, you need a test image. In fact, you can reuse the image from that tip -- you can find the image here. In the code examples below, the image name is set to test.jpg. The image should be in the directory in which you run these examples.
To begin, let\'s create a framework for these examples. The program below, ExampleFramework, is similar to the example code used in the ConvolveOp Tech Tip. As in the code examples for the earlier tip, ExampleFramework uses a simple JFrame that holds the image, and uses a JSlider. However to make it easy to plug in a variety of filters and transforms, the code related to the specific effect has been removed, and accessor methods have been inserted. For consistency, the processed image will be referred to as filteredImage, whether the change is the result of applying a filter or a transform.
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.ImageIcon;
import javax.swing.JSlider;
import javax.swing.event.ChangeListener;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.BorderLayout;
import java.awt.image.BufferedImage;
public class ExampleFramework extends JPanel {
private BufferedImage originalImage;
private BufferedImage filteredImage;
private JSlider slide = new JSlider(1, 50, 25);
private int height, width;
ExampleFramework(String titlebar) {
createBufferedImages();
setUpJFrame(titlebar);
}
private void createBufferedImages() {
Image image =
new ImageIcon(\"test.jpg\").getImage();
height = image.getHeight(null);
width = image.getWidth(null);
originalImage =
new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
filteredImage = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics g = originalImage.createGraphics();
g.drawImage(image, 0, 0, null);
g.dispose();
}
private void setUpJFrame(String titlebar) {
JFrame frame = new JFrame(titlebar);
frame.setSize(filteredImage.getWidth(),
filteredImage.getHeight());
frame.getContentPane().setLayout
(new BorderLayout());
frame.getContentPane().add
(this, BorderLayout.CENTER);
frame.getContentPane().add
(slide, BorderLayout.SOUTH);
frame.setResizable(false);
frame.setDefaultCloseOperation
(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
// accessor methods for plugging in filters
public void setChangeListener(ChangeListener cl) {
slide.addChangeListener(cl);
}
public void setFilteredImage
(BufferedImage image) {
filteredImage = image;
repaint();
}
public int getSlideValue() {
return slide.getValue();
}
public BufferedImage getOriginal() {
return originalImage;
}
public void paintComponent(Graphics g) {
g.clearRect(0, 0, width, height);
g.drawImage(filteredImage, 0, 0, this);
}
}
As a first example, let\'s use an affine transformation to zoom the image in and out. You might want to refer to the September 9, 2003 Tech Tip Understanding AffineTransform for some of the mathematical details behind such transforms. You will create a new instance of an AffineTransformOp, and pass in two arguments. You will then produce the new image from the old image using the AffineTransformOp that you created. Finally, you will tell the ExampleFramework object to update the displayed image.
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