How to make Canvas draw area transparent in android?

Question

I would like to make Canvas area transparent because I would like to add an Image behind it so that Canvas actions happen above the image.My code for the canvas is here

Answer 1

I got the output by this

 public Panel(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    this.setBackgroundColor(Color.TRANSPARENT);                 
    this.setZOrderOnTop(true); //necessary                
    getHolder().setFormat(PixelFormat.TRANSPARENT); 
    getHolder().addCallback(this); 
    mThread = new ViewThread(this); 

}