opencv中测量运行时间的函数

  最开始的C接口中的是 cvGetTickCount()和 cvGetTickFrequency()，在程序段的开始和结束时两次使用cvGetTickCount()，然后将两次的差除以cvGetTickFrequency()后就可以获得程序段的以微秒us为单位的运行时间，不是很精确但是一般足够了。

         到了2.x之后在命名空间cv中又多了几个函数，getTickCount()，getTickFrequency()，getCPUTickCount()，此时仍然可以使用上面的C接口的函数，也可以使用这几个namespace cv中的函数，两次使用getTickCount()，然后再除以getTickFrequency()，不过需要注意的是这时计算出来的是以秒s为单位的时间，这个是与上面的带cv前缀的函数的不同，而要使用更精确的计时，就需要使用getCPUTickCount()，不过现代计算机CPU的频率会随着负载而变化所以没大有必要使用该函数，可以参看函数的介绍【Also, since a modern CPU varies the CPU frequency depending on the load, the number of CPU clocks spent in some code cannot be directly converted to time units. Therefore,getTickCount is generally a preferable solution for measuring execution time.】也就是使用getTickCount就足够了。

        同时C++接口中还将上面的函数封装为了一个类TickMeter，方便使用，下面是关于TickMeter的声明和实现的源码：

//contrib.hpp
class CV_EXPORTS TickMeter
{
public:
    TickMeter();
    void start();
    void stop();

    int64 getTimeTicks() const;
    double getTimeMicro() const;
    double getTimeMilli() const;
    double getTimeSec()   const;
    int64 getCounter() const;

    void reset();
private:
    int64 counter;
    int64 sumTime;
    int64 startTime;
};
CV_EXPORTS std::ostream& operator<<(std::ostream& out, const TickMeter& tm);

//Spinimages.cpp
cv::TickMeter::TickMeter() { reset(); }
int64 cv::TickMeter::getTimeTicks() const { return sumTime; }
double cv::TickMeter::getTimeMicro() const { return (double)getTimeTicks()/cvGetTickFrequency(); }
double cv::TickMeter::getTimeMilli() const { return getTimeMicro()*1e-3; }
double cv::TickMeter::getTimeSec()   const { return getTimeMilli()*1e-3; }
int64 cv::TickMeter::getCounter() const { return counter; }
void  cv::TickMeter::reset() {startTime = 0; sumTime = 0; counter = 0; }

void cv::TickMeter::start(){ startTime = cvGetTickCount(); }
void cv::TickMeter::stop()
{
    int64 time = cvGetTickCount();
    if ( startTime == 0 )
        return;

    ++counter;

    sumTime += ( time - startTime );
    startTime = 0;
}

std::ostream& cv::operator<<(std::ostream& out, const TickMeter& tm){ return out << tm.getTimeSec() << "sec"; }

//contrib.hpp  
class CV_EXPORTS TickMeter
{
public:
	TickMeter();
	void start();
	void stop();

	int64 getTimeTicks() const;
	double getTimeMicro() const;
	double getTimeMilli() const;
	double getTimeSec()   const;
	int64 getCounter() const;

	void reset();
private:
	int64 counter;
	int64 sumTime;
	int64 startTime;
};
CV_EXPORTS std::ostream& operator<<(std::ostream& out, const TickMeter& tm);

//Spinimages.cpp	
cv::TickMeter::TickMeter() { reset(); }
int64 cv::TickMeter::getTimeTicks() const { return sumTime; }
double cv::TickMeter::getTimeMicro() const { return (double)getTimeTicks()/cvGetTickFrequency(); }
double cv::TickMeter::getTimeMilli() const { return getTimeMicro()*1e-3; }
double cv::TickMeter::getTimeSec()   const { return getTimeMilli()*1e-3; }    
int64 cv::TickMeter::getCounter() const { return counter; }
void  cv::TickMeter::reset() {startTime = 0; sumTime = 0; counter = 0; }

void cv::TickMeter::start(){ startTime = cvGetTickCount(); }
void cv::TickMeter::stop()
{
	int64 time = cvGetTickCount();
	if ( startTime == 0 )
		return;

	++counter;

	sumTime += ( time - startTime );
	startTime = 0;
}

std::ostream& cv::operator<<(std::ostream& out, const TickMeter& tm){ return out << tm.getTimeSec() << "sec"; }

 

           可以看出TickMeter仅仅是将C接口的函数进行了一下封装，不过使用时就方便多了，不用去反复gettickcount然后除以frequency了，只需要在开始时调用start()；结束时调用stop()，然后如果需要以us为单位的运行时间就调用getTimeMicro()，以ms为单位的就调用getTimeMilli()，以s为单位的是getTimeSec()，而getTimeTicks()返回运行时间的tickcount，getTimeTicks()返回的是调用stop的次数，同时该类还重载了ostream，可以方便的以s为单位直接输出。

一个小例子：

TickMeter tm;
tm.start();
    int col=temp.cols, row = temp.rows;
    if (temp.isContinuous())
    {
        col*=row;
        row =1;
    }
    for (i=0; i<row; ++i)
    {
        const float *pt = temp.ptr<float>(i);
        for (j=0; j<col;++j)
        {
            float mm=pt[3*j];
            mm = mm/(float)20.6;
        }
    }
    tm.stop();
    cout<<"count="<<tm.getCounter()<<",process time="<<tm.getTimeMilli()<<endl;

TickMeter tm;	
tm.start();
	int col=temp.cols, row = temp.rows;
	if (temp.isContinuous())
	{
		col*=row;
		row =1;
	}
	for (i=0; i<row; ++i)
	{
		const float *pt = temp.ptr<float>(i);
		for (j=0; j<col;++j)
		{
			float mm=pt[3*j];
			mm = mm/(float)20.6;
		}
	}
	tm.stop();
	cout<<"count="<<tm.getCounter()<<",process time="<<tm.getTimeMilli()<<endl;