ImageIO.write 仅在 Java 中的 png 中起作用的镜像图像

Question

I was using ImageIO to write a mirror image to the local file. However, I found that the mirrored image file would be created only if I wrote the image to png file. Please note that the original image was in jpg format. If I change the ImageIO.write format to "jpg" or some formats other than "png", no image file would be created.

BufferedImage image = null;
URL url = null;
String link = "http://www.fullerton.edu/_resources/images/empowerment-james.jpg";
try {

    url = new URL(link);
    image = ImageIO.read(url);
    width = image.getWidth();
    height = image.getHeight();

    BufferedImage mirror = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);

    for (int y = 0; y < height; y++) {
        for (int lx = 0, rx = width - 1; lx < width; lx++, rx--) {
            int lp = image.getRGB(lx, y);

            mirror.setRGB(rx, y, lp);

        }
    }
    JFrame frame2 = new JFrame();
    frame2.setSize(width + offset, height + offset);
    JLabel label2 = new JLabel(new ImageIcon(mirror));
    frame2.add(label2);
    frame2.setVisible(true);
    file = new File("mirror.png");

    ImageIO.write(mirror, "png", file);
} catch (IOException e) {
    System.out.println(e.getMessage());
}

Answer 1

So, beware, not all image formats will support transparency (ie BufferedImage.TYPE_INT_ARGB ), so, make sure you actually know where the file is been written, it might "appear" as it's not getting written, but it might be getting written to some place you're not expecting.

So, the following example works just fine, pay attention to the output at the end of the file, it's telling the directory the images were written to.

import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class Main {
    public static void main(String[] args) {
        try {
            new Main();
        } catch (IOException ex) {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public Main() throws MalformedURLException, IOException {
        BufferedImage original = ImageIO.read(new URL("http://www.fullerton.edu/_resources/images/empowerment-james.jpg"));
        BufferedImage mirrored = new BufferedImage(original.getWidth(), original.getHeight(), original.getTransparency());
        Graphics2D g2d = mirrored.createGraphics();
        g2d.setTransform(AffineTransform.getScaleInstance(-1, 1));
        g2d.drawImage(original, -original.getWidth(), 0, null);
        g2d.dispose();

        JPanel panel = new JPanel();
        panel.add(new JLabel(new ImageIcon(original)));
        panel.add(new JLabel(new ImageIcon(mirrored)));

        JOptionPane.showMessageDialog(null, panel);

        System.out.println("Writing to " + System.getProperty("user.dir"));

        ImageIO.write(mirrored, "png", new File("Test.png"));
        ImageIO.write(mirrored, "jpg", new File("Test.jpg"));
    }


}