BufferedImage from PNG : Alpha Channel disregaurded

Question

I'm trying to load a PNG with an alpha channel into a BufferedImage, and
then sample the BufferedImage at various pixels for some operations.
However, the alpha channel seems to get lost upon creation of the BufferedImage.
For example, I'm using a PNG that is 100% transparent, and when I
load it into a BufferedImage and display it on a panel all I see is the panel's background color.
So far so good. Now, the problem. When I try to sample a pixel, the alpha is always 255 or 100% opaque
which is clearly not right. Also, when I print out the BufferedImage's type, I get 0 which means the image
type is "Custom". Care to shed any light as to how I can accurately sample an image with an alpha channel?
import javax.swing.*;
import java.awt.*;
import java.io.*;
import javax.imageio.*;
import java.awt.image.*;
public class PNGTest extends JFrame {
    public PNGTest() {
        setLocation(500,500);
        BufferedImage img = new BufferedImage(640,480,BufferedImage.TYPE_INT_RGB);
        try {
            img = ImageIO.read(new File("C:/folder/folder/myPNG.png"));
        } catch (Exception e) {
        setSize(img.getWidth(), img.getHeight());
        getContentPane().setBackground(Color.white);
        getContentPane().add(new JLabel(new ImageIcon(img)));
        setVisible(true);
        //Sample top left pixel of image and pass it to a new color
        Color color = new Color(img.getRGB(0,0));
        //print the alpha of the color
        System.out.println(color.getAlpha());
        //print the type of the bufferedimage
        System.out.println(img.getType());
    public static void main(String[] args) {
        new PNGTest();
}Edited by: robbie.26 on May 20, 2010 4:26 PM
Edited by: robbie.26 on May 20, 2010 4:26 PM
Edited by: robbie.26 on May 20, 2010 4:29 PM

Answer 1

Here ya go robbie, ti seems to work for the rest of the world, but not for you:
import java.awt.*;
import java.awt.image.*;
import java.net.URL;
import javax.swing.*;
import javax.imageio.*;
public class JTransPix{
  JTransPix(){
    JFrame f = new JFrame("Forum Junk");
    JPanel p = new MyJPanel();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.add(p);
    f.pack();
    f.setVisible(true);
  public static void main(String[] args) {
    new JTransPix();
  class MyJPanel extends JPanel{
    BufferedImage bi = null;
    MyJPanel(){
      try{
        bi = ImageIO.read(new URL("http://upload.wikimedia.org/wikipedia/commons/archive/4/47/20100130232511!PNG_transparency_demonstration_1.png"));  //here ya go--one liner
        this.setPreferredSize(new Dimension(bi.getWidth(), bi.getHeight()));
      }catch(java.io.IOException e){
        System.out.println(e.toString());
    public void paintComponent(Graphics g){
      super.paintComponent(g);
      g.setColor(Color.BLUE);
      g.fillRect(0, 0, bi.getWidth(), bi.getHeight());
      g.drawImage(bi,0, 0, this);
}Please notice how the BufferedImage is declared and set to NULL, then allow ImageIO to set the type--Just as I said before. If you have any question about the PNG producing an ARGB image with ImageIO, then change the color painted onto the backgroun din the paintComponent to what ever you want and you'll see it show through.
BTW: even in the short nobrainers--you still need to have VALID CATCH BLOCKS.
To get what you are looking for, you can mask off the Alpha component by dividing each getRGB by 16777216 (256^3) or do a binary shift right 24 places.