这段代码如何能改成图片现实背景呢？求大神指教

public static Bitmap createImage(Drawable tile, int w, int h) {
Bitmap bitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
tile.setBounds(0, 0, w, h);
tile.draw(canvas);
return bitmap;
}

怎么又有bitmap又有canvas？