在进行程序的界面设计时，常常希望将位图的关键部分，也即图像的前景显示在界面上，而将位图的背景隐藏起来，将位图与界面很自然的融合在一起。-At the time of the interface design of the program, often want to key parts of the bitmap, that is the foreground of the image displayed in the interface, and a bitmap background hidden, bitmap and the interface is very natural together.