Java - Achieving Partial Transperancy

I'm trying to achieve partial transperancy in Java. The easy approach would be using .png, this however, is not hardware accelerated(I draw the images with Graphics2D), and does tend to be very slow. Is there a way to change the alpha channel of an image in Java? I read something about Bit Shifting somewhere, but I'm really not skilled enough to write code to do that... At least I don't think I am...

Thanks in advance!