OpenCV 利用getTickCount()与getTickFrequency()计算执行时间

Bertha 。 2022-06-16 01:07 125阅读 0赞

其实这是个很简单的应用，贴出来是因为我经常能用到这两个函数，顺便写一下吧。

double t1 = (double)getTickCount();
    .
    .
    .
    double t2 = (double)getTickCount();
    cout<<"time:"<<(t2-t1)*1000/(getTickFrequency())<<endl;

getTickCount()与getTickFrequency()都被定义在core.hpp文件下：

//! Returns the number of ticks.
    
    /*!
      The function returns the number of ticks since the certain event (e.g. when the machine was turned on).
      It can be used to initialize cv::RNG or to measure a function execution time by reading the tick count
      before and after the function call. The granularity of ticks depends on the hardware and OS used. Use
      cv::getTickFrequency() to convert ticks to seconds.
    */
    CV_EXPORTS_W int64 getTickCount();
    
    /*!
      Returns the number of ticks per seconds.
    
      The function returns the number of ticks (as returned by cv::getTickCount()) per second.
      The following code computes the execution time in milliseconds:
    
      \code
      double exec_time = (double)getTickCount();
      // do something ...
      exec_time = ((double)getTickCount() - exec_time)*1000./getTickFrequency();
      \endcode
    */
    CV_EXPORTS_W double getTickFrequency();
    
    /*!
      Returns the number of CPU ticks.
    
      On platforms where the feature is available, the function returns the number of CPU ticks
      since the certain event (normally, the system power-on moment). Using this function
      one can accurately measure the execution time of very small code fragments,
      for which cv::getTickCount() granularity is not enough.
    */
    CV_EXPORTS_W int64 getCPUTickCount();

getTickCount()：用于返回从操作系统启动到当前所经的计时周期数，看名字也很好理解，get Tick Count(s)。  
getTickFrequency()：用于返回CPU的频率。get Tick Frequency。这里的单位是秒，也就是一秒内重复的次数。

所以剩下的就很清晰了：  
总次数/一秒内重复的次数 = 时间(s)  
1000 \*总次数/一秒内重复的次数= 时间(ms)

这个逻辑很清晰，没什么问题，但是这里有一个小坑，那就是C版本的cvGetTickFrequency()函数和C++版本的getTickFrequency()的单位不一样，前者以ms计算频率，后者以s为单位计算频率，所以如果使用C版本的cvGetTickFrequency()计算时间的话，应该是：  
总次数/一秒内重复的次数*1000 = 时间(ms)  
总次数/一秒内重复的次数*1000000 = 时间(s)