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 spots of noise, multiplicative noise is added to the equation f = f+n* f to the image f, where n is zero mean, variance var, uniformly distributed random noise.)