Measure OpenCV FPS

Question

I\'m looking for a correct way to measure openCV FPS. I\'ve found several ways to do it. but none of them looks right for me.

The first one I\'ve tested, uses ti

Answer 1

I would just measure the walltime and simply divide the frames by time elapsed. On linux:

/*
* compile with:
*   g++ -ggdb webcam_fps_example2.cpp -o webcam_fps_example2 `pkg-config --cflags --libs opencv`
*/

#include "opencv2/opencv.hpp"
#include <time.h>
#include <sys/time.h>


using namespace cv;
using namespace std;

double get_wall_time(){
    struct timeval time;
    if (gettimeofday(&time,NULL)){
        //  Handle error
        return 0;
    }
    return (double)time.tv_sec + (double)time.tv_usec * .000001;
}


int main(int argc, char** argv)
{
    VideoCapture cap;
    // open the default camera, use something different from 0 otherwise;
    // Check VideoCapture documentation.
    if(!cap.open(0))
        return 0;

    cap.set(CV_CAP_PROP_FRAME_WIDTH,1920);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT,1080);

    double wall0 = get_wall_time();
    for(int x = 0; x < 500; x++)
    {
          Mat frame;
          cap >> frame;
          if( frame.empty() ) break; // end of video stream
          //imshow("this is you, smile! :)", frame);
          if( waitKey(10) == 27 ) break; // stop capturing by pressing ESC 
    }
    double wall1 = get_wall_time();
    double fps = 500/(wall1 - wall0);
    cout << "Wall Time = " << wall1 - wall0 << endl;
    cout << "FPS = " << fps << endl;
    // the camera will be closed automatically upon exit
    // cap.close();
    return 0;
}

Wall Time = 43.9243 FPS = 11.3832

Answer 2

You can use OpenCV's API to get the original FPS if you are dealing with video files. The following method will not work when capturing from a live stream:

cv::VideoCapture capture("C:\\video.avi");
if (!capture.isOpened())
{
    std::cout  << "!!! Could not open input video" << std::endl;
    return;
}

std::cout << "FPS: " << capture.get(CV_CAP_PROP_FPS) << std::endl;

To get the actual FPS after the processing, you can try Zaw's method.

Answer 3

I have posted a way to do that @ Getting current FPS of OpenCV. It is necessary to do a bit of averaging otherwise the fps will be too jumpy.

edit

I have put a Sleep inside process() and it gives correct fps and duration(+/- 1ms).

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <opencv/cv.h>
#include <sys/timeb.h>
using namespace cv;

#if defined(_MSC_VER) || defined(WIN32)  || defined(_WIN32) || defined(__WIN32__) \
    || defined(WIN64)    || defined(_WIN64) || defined(__WIN64__) 

#include <windows.h>
bool _qpcInited=false;
double PCFreq = 0.0;
__int64 CounterStart = 0;
void InitCounter()
{
    LARGE_INTEGER li;
    if(!QueryPerformanceFrequency(&li))
    {
        std::cout << "QueryPerformanceFrequency failed!\n";
    }
    PCFreq = double(li.QuadPart)/1000.0f;
    _qpcInited=true;
}
double CLOCK()
{
    if(!_qpcInited) InitCounter();
    LARGE_INTEGER li;
    QueryPerformanceCounter(&li);
    return double(li.QuadPart)/PCFreq;
}

#endif

#if defined(unix)        || defined(__unix)      || defined(__unix__) \
    || defined(linux)       || defined(__linux)     || defined(__linux__) \
    || defined(sun)         || defined(__sun) \
    || defined(BSD)         || defined(__OpenBSD__) || defined(__NetBSD__) \
    || defined(__FreeBSD__) || defined __DragonFly__ \
    || defined(sgi)         || defined(__sgi) \
    || defined(__MACOSX__)  || defined(__APPLE__) \
    || defined(__CYGWIN__) 
double CLOCK()
{
    struct timespec t;
    clock_gettime(CLOCK_MONOTONIC,  &t);
    return (t.tv_sec * 1000)+(t.tv_nsec*1e-6);
}
#endif

double _avgdur=0;
double _fpsstart=0;
double _avgfps=0;
double _fps1sec=0;

double avgdur(double newdur)
{
    _avgdur=0.98*_avgdur+0.02*newdur;
    return _avgdur;
}

double avgfps()
{
    if(CLOCK()-_fpsstart>1000)      
    {
        _fpsstart=CLOCK();
        _avgfps=0.7*_avgfps+0.3*_fps1sec;
        _fps1sec=0;
    }
    _fps1sec++;
    return _avgfps;
}

void process(Mat& frame)
{
    Sleep(3);
}
int main(int argc, char** argv)
{
    int frameno=0;
    cv::Mat frame;
    cv::VideoCapture cap(0);
    for(;;)
    {
        //cap>>frame;
        double start=CLOCK();
        process(frame);
        double dur = CLOCK()-start;
        printf("avg time per frame %f ms. fps %f. frameno = %d\n",avgdur(dur),avgfps(),frameno++ );
        if(waitKey(1)==27)
            exit(0);
    }
    return 0;
}    

Answer 4

You can use opencv helper cv::getTickCount()

#include <iostream>
#include <string>

#include "opencv2/core.hpp"
#include "opencv2/core/utility.hpp"
#include "opencv2/video.hpp"
#include "opencv2/highgui.hpp"

using namespace cv;


int main(int ac, char** av) {

    VideoCapture capture(0);
    Mat frame;

    for (;;) {

        int64 start = cv::getTickCount();

        capture >> frame;
        if (frame.empty())
            break;

        /* do some image processing here */

        char key = (char)waitKey(1);

        double fps = cv::getTickFrequency() / (cv::getTickCount() - start);
        std::cout << "FPS : " << fps << std::endl;
    }
    return 0;
}