显示图像后，单击鼠标左键连出完全背景区域，双击左键结束；

图像改变后，再单击鼠标左键连出完全前景区域，双击左键结束。即可得到结果

-Display the image, click the left mouse button to even out completely the background area, double-click the left end　images after the change, and then click the left mouse button even a completely foreground area, double-click the left button ending. The results can be obtained