OpenCV 提供一个函数 getTickCount() ，能够用来測量一段代码的执行时间。另一个函数 getTickFrequency() 用来返回每秒内的时钟周期。代码操作例如以下：

double duration;  duration = static_cast
     
      (getTickCount());  colorReduce(src);  duration = static_cast
      
       (getTickCount()) - duration;  duration /= getTickFrequency();//执行时间以ms为单位
      
     

通过时间计算函数。对上小节中的像素引用方法做出对照。终于得出运算速度最快的 colorReduce() 函数。代码例如以下：

#include 
     
        #include 
      
         #include 
       
            using namespace cv;    void colorReduce(Mat &source, int div = 64)  {      int row = source.rows;      int rowN = source.cols;      if ( source.isContinuous() )//检測图像内存是否连续      {          rowN = rowN * row;          row = 1;      }        for ( int j = 0; j < row; j ++ )      {          uchar* data = source.ptr
        
         (j);          for ( int i = 0; i < rowN; i ++ )          {              *data = *data/div*div + div/2;              data++;              *data = *data/div*div + div/2;              data++;              *data = *data/div*div + div/2;              data++;          }      }  }    int main()  {      Mat src = imread("lena.jpg",1);      colorReduce(src);      namedWindow("src",0);      imshow("src",src);      waitKey(0);      return 0;  }