说明：  均值滤波是典型的线性滤波算法，它是指在图像上对目标像素给一个模板，该模板包括了其周围的临近像素（以目标象素为中心的周围8个像素，构成一个滤波模板，即去掉目标像素本身），再用模板中的全体像素的平均值来代替原来像素值。
(Mean filter is a typical linear filtering algorithm, it refers to the target pixel in the image to a template that includes the surrounding adjacent pixels (peripheral to the target pixel as the center of eight pixels to form a filter template, namely remove the target pixel itself), then the average of all the pixels in the template to replace the original pixel values.)