Changing Image Opacity

Question

In a project, I want to simultaneously resize and change the opacity of an image. So far I think I've got the resizing down. I use a method defined like so to accomplish the resizing:

public BufferedImage resizeImage(BufferedImage originalImage, int type){

    initialWidth += 10;
    initialHeight += 10;
    BufferedImage resizedImage = new BufferedImage(initialWidth, initialHeight, type);
    Graphics2D g = resizedImage.createGraphics();
    g.drawImage(originalImage, 0, 0, initialWidth, initialHeight, null);
    g.dispose();

    return resizedImage;
} 

I got this code from here. What I can't find a solution to is changing the opacity. That's what I'm wondering how to do (if it's possible at all). Thanks in advance.

UPDATE:

I tried this code to display a picture of a circle with transparent insides and outsides (see below image) growing and becoming less and less opaque, but it didn't work. I'm not sure what's wrong. All the code is in a class called Animation

public Animation() throws IOException{

    image = ImageIO.read(new File("circleAnimation.png"));
    initialWidth = 50;
    initialHeight = 50;
    opacity = 1;
}

public BufferedImage animateCircle(BufferedImage originalImage, int type){

      //The opacity exponentially decreases
      opacity *= 0.8;
      initialWidth += 10;
      initialHeight += 10;

      BufferedImage resizedImage = new BufferedImage(initialWidth, initialHeight, type);
      Graphics2D g = resizedImage.createGraphics();
      g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
      g.drawImage(originalImage, 0, 0, initialWidth, initialHeight, null);
      g.dispose();

      return resizedImage;

}

I call it like this:

Animation animate = new Animation();
int type = animate.image.getType() == 0? BufferedImage.TYPE_INT_ARGB : animate.image.getType();
BufferedImage newImage;
while(animate.opacity > 0){

    newImage = animate.animateCircle(animate.image, type);
    g.drawImage(newImage, 400, 350, this);

}

Solution

first make sure the type you're passing into to method contains an alpha channel, like

BufferedImage.TYPE_INT_ARGB

and then just before you paint the new image, call the Graphics2D method setComposite like so:

float opacity = 0.5f;
g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));

that will set the drawing opacity to 50%.

Comments

[Andrew Thompson]

For better help sooner, post an SSCCE.

[pasawaya]

Also, just checking, does 1 correspond to completely visible and 0 to transparent? Thanks. And also, do I call setComposite() before or after I draw?

[MadProgrammer]

0 is transparent, 1 is opaque

[tom]

the code you posted will reduce the opacity to 0 too fast to see, so either increase the reduction factor of the opacity to like 0.999 or just call Thread.sleep in the while loop so you can see your code working. Oh and yes 0 is transparent 1 is opaque, and yes you call setComposite before you draw.