说明：  用于图像边缘的羽化操作。假设有两幅图像，一幅是前景，一幅是背景。源代码为matlab，是将前景图像的边缘向背景过渡的操作。
(Feathering operation for image edge. Suppose there are two images, one is the foreground, a background. The source code for matlab, is a transitional operation of the edges of the image of the foreground to the background.)