How to make an image as transparent in BlackBerry?

I am new to BlackBerry Java application 开发者_开发问答development. My scenario is: In my application a gallery list of images will be displayed in a small icons. If I click on any image it will display in a large mode. Here I need to provide controls like front and back buttons. On clicking on those buttons the background image should change. In addition to that those buttons should be highlighted and the back ground large image should be transparent. How to do this?

Please guide me.

You can use Graphics.setGlobalAlpha() on paint() or to modify bitmap before preview.
Don't forget to set back normal global alpha value after bitmap drawing.