speckle

代码说明：

  对图像进行斑点噪声的添加，用方程f=f+n*f将乘性噪音添加到图像f上，其中n是均值为零，方差为var的均匀分布的随机噪声。(Image speckle noise addition, the equation f = f+ N* f will be added to the multiplicative noise on the image f, in which n is zero mean, variance var of the uniform distribution for the random noise.)