如何将动态创建的BufferedImage实例的背景设置为透明？

Question

I am trying to create a BufferedImage instance which contains a rounded rectangle of a certain colour and is transparent everywhere else.

I am using the following code to create the image

 private BufferedImage createChromImage() {
    BufferedImage I = new BufferedImage(350, 20, ColorSpace.TYPE_RGB);
    Graphics2D g2 = I.createGraphics();

    g2.setPaint(new GradientPaint(0, 0, Color.DARK_GRAY, 100,
              100, Color.BLUE, false));

    g2.fillRoundRect(0, 0, 350, 20, 10, 10);

    return I;
 }

I end up with a rounded rectangle on a black background, is there a way in which I can get it on a transparent background. I suspect it will require a different ColorSpace setting, but I not sure which.. any help is much appreciated.

Answer 1

You can't have a transparent background in an image that does not support transparency. RGB is a 24-bit image with no transparency. Instead, you want to use BufferedImage.TYPE_INT_ARGB as the argument to BufferedImage's constructor: that will give you an alpha channel to play with, which will allow transparency.