背景减法库（BGS Library = background subtraction library）包含了37种背景建模算法，也是目前国际上关于背景建模技术研究最全也最权威的资料。本文将更加详细的介绍背景减法库（BGS Library）的基本框架与入口函数main()的功能。

BGS库的整体框架在背景建模技术（二）中已经全部给出，此处从函数的角度再次给出BGS库的基本框架，有利于代码的修改与维护。

如下图所示是基于C++的BGS库的函数流程图：

接下来将会对每个函数进行更加详细的分析。

首先，先看入口函数main()，代码如下：

#include "Config.h"
#include "VideoAnalysis.h"
#include <iostream>

using namespace std;

namespace bgslibrary
{
	class Main
	{
		private:
		Main();

		public:
		static void start(int argc, const char **argv)
		{
			cout << "-----------------------------------------" << endl;
			cout << "Background Subtraction Library v1.9.2     " << endl;
			cout << "http://code.google.com/p/bgslibrary       " << endl;
			cout << "by:                                       " << endl;
			cout << "Andrews Sobral (andrewssobral@gmail.com)  " << endl;
			cout << "Optimized by:                             " << endl;
			cout << "Rui-Dong Fang(National Huaqiao University)" << endl;
			cout << "-----------------------------------------" << endl;
			cout << "Using OpenCV version " << CV_VERSION << endl;

			try
			{
				int key = KEY_ESC;

				do
				{
					VideoAnalysis* videoAnalysis = new VideoAnalysis;

					if (videoAnalysis->setup(argc, argv))	///videoAnalysis->setup(argc, argv)
					{
						videoAnalysis->start();

						cout << "Processing finished, enter:" << endl;
						cout << "R - Repeat" << endl;
						cout << "Q - Quit" << endl;

						key = cv::waitKey();
					}

					cv::destroyAllWindows();
					delete videoAnalysis;

				} 
				while (key == KEY_REPEAT);
			}
			catch (const std::exception& ex)
			{
				cout << "std::exception:" << ex.what() << endl;
				return;
			}
			catch (...)
			{
				cout << "Unknow error" << endl;
				return;
			}

#ifdef WIN32
	//system("pause");
#endif
		}
	};
}

int main(int argc, const char **argv)
{
	bgslibrary::Main::start(argc, argv);
	return 0;
}

在main（）函数中，除了打印出相关信息和设置waitKey（）以外，主要就是调用了VIdeoAnalysis.cpp（将在下一篇博文中分析）中的videoAnalysis->setup(argc, argv)和videoAnalysis->start()。下面给出Main.cpp的代码流程图：