说明：  利用中值法，在一系列的视频序列中提取初始背景，一般在视频处理中，作为初始背景，这是提取背景，实时更新的一个前提；
(Using the value method, in a series of video sequences to extract the initial background, usually in the video processing, as the initial background, which is extracted the background, a prerequisite for real-time updates )