Android : ZoomIn and ZoomOut using Canvas

Question

How to Zoom-In and Zoom-Out Image using Canvas.

class DrawOval extends View {
private Bitmap leftimage = BitmapFactory.decodeResource(getResources(),R.drawable.box);
private Bitmap left = Bitmap.createScaledBitmap(leftimage, w1, h1, true);

    public DrawOval(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }
    protected synchronized void onDraw(Canvas canvas) {
        }
}

I am draw the image using Bitmap. I want to Zoom-In and Zoom-Out image. If anyone know Tell me idea to do that.