说明：  这个matlab程序实现的是一个噪声生成器，它可以生成高斯、椒盐、加性及乘性噪声，并把这些噪声添加到一幅图像上。
(Matlab implementation of this process is a noise generator, it can generate Gaussian, salt and pepper, additive and multiplicative noise, and noise is added to put these on an image.)