如何实现透明遮挡层显示图片

实现透明遮挡层显示图片（效果如下）

Context context = ManualActivity.this;
Dialog dia = new Dialog(context, R.style.edit_AlertDialog_style);
dia.setContentView(R.layout.activity_start_dialog);
ImageView imageView = (ImageView) dia.findViewById(R.id.img_manual_example);
imageView.setBackgroundResource(R.drawable.manual_idcard);
dia.show();
dia.setCanceledOnTouchOutside(true); // Sets whether this dialog is
Window w = dia.getWindow();

WindowManager.LayoutParams lp = w.getAttributes();
lp.x = 0;
lp.y = 40;
dia.onWindowAttributesChanged(lp);