Question

我面临着第一次使用opencv（3.0）调整大小功能的缓慢执行时间（在Windows上使用visual studio）。以下简单程序显示了问题：

int _tmain(int argc, _TCHAR* argv[])
{
   DECLARE_TIMING(ttt);
   START_TIMING(ttt);
   cv::Mat tmp1=cv::Mat::ones(100,100, CV_8UC3);
   cv::Mat res1=cv::Mat::zeros(100*0.25, 100*0.25, CV_8UC3);
   cv::resize(tmp1, res1, cv::Size(0,0), 0.25f, 0.25f, CV_INTER_AREA);
   STOP_TIMING(ttt);
   double runTime = GET_TIMING(ttt);
   std::cout << "First resize run time = " << runTime << " mSec\n"; 

   START_TIMING(ttt);
   cv::Mat tmp2=cv::Mat::ones(100,100, CV_8UC3);
   cv::Mat res2=cv::Mat::zeros(100*0.25, 100*0.25, CV_8UC3);
   cv::resize(tmp2, res2, cv::Size(0,0), 0.25f, 0.25f, CV_INTER_AREA);
   STOP_TIMING(ttt);
   runTime = GET_TIMING(ttt);
   std::cout << "Second resize run time = " << runTime << " mSec\n";    

   return 0;

}

结果是：

First resize run time = 259.575 mSec
Second resize run time = 0.0769735 mSec

现在为什么第一次调整大小的时间需要259毫秒，而第二次调整则需要更少？（注意，我知道不需要res1和res2的预分配，这是我努力克服这个问题的一部分）

Answer 1

我怀疑这与函数static内的cv::resize变量初始化有关。

static ResizeFunc linear_tab[] = ...
static ResizeFunc cubic_tab[] = ...
static ResizeFunc lanczos4_tab[] =
static ResizeAreaFastFunc areafast_tab[] = ...
static ResizeAreaFunc area_tab[] = ...

The static variables are initialized the first time execution hits their declaration

这是一个相当于您的代码段，没有宏或Windows相关的东西。您可以看到，如果您将第一个虚拟调用取消注释为resize，则以下调用的执行时间几乎相同。

#include <opencv2\opencv.hpp>
#include <iostream>
using namespace cv;
using namespace std;

int main()
{
    // Dummy call to initialize static variables.
    //resize(Mat1b(1, 1), Mat1b(1, 1), Size(1, 1));

    cv::Mat tmp1 = cv::Mat::ones(100, 100, CV_8UC3);
    cv::Mat res1 = cv::Mat::zeros(100 * 0.25, 100 * 0.25, CV_8UC3);

    double tic1 = double(getTickCount());
    cv::resize(tmp1, res1, cv::Size(0, 0), 0.25f, 0.25f, CV_INTER_AREA);
    double toc1 = (double(getTickCount()) - tic1) * 1000.0 / getTickFrequency();
    std::cout << "First resize run time = " << toc1 << " ms" << std::endl;


    cv::Mat tmp2 = cv::Mat::ones(100, 100, CV_8UC3);
    cv::Mat res2 = cv::Mat::zeros(100 * 0.25, 100 * 0.25, CV_8UC3);

    double tic2 = double(getTickCount());
    cv::resize(tmp2, res2, cv::Size(0, 0), 0.25f, 0.25f, CV_INTER_AREA);
    double toc2 = (double(getTickCount()) - tic2) * 1000.0 / getTickFrequency();
    std::cout << "Second resize run time = " << toc2 << " ms" << std::endl;

    getchar();

    return 0;
}

慢opencv调整函数执行时间

1 个答案: