1. cvGetTickCount()和cvGetTickFrequency()计时，得到的单位是us级的统计时间：
double start = static_cast<double>(cvGetTickCount());
double time = ((double)cvGetTickCount() - start) / cvGetTickFrequency();
cout << "所用时间:" << time << "us" << endl;
cout << "所用时间为:" << time/1000 << "ms" << endl;
2. getTickCount()和getTickFrequency()，得到的单位是s级的统计时间：
double start = static_cast<double>(getTickCount());
double time = ((double)getTickCount() - start) / getTickFrequency();
cout << "所用时间为：" << time << "秒" << endl;