中文说明：此文档中的代码可以计算5种图像的质量参数，分别是：图像灰度均值、图像方差、图像平均梯度、熵和峰值信噪比及均方误差。
English Description：
The code in this document can calculate five kinds of image quality parameters, which are: image gray mean, image variance, image average gradient, entropy, peak signal-to-noise ratio and mean square error.