4/25/2014

(OpenCV Study) calcOpticalFlowFarneback example source code ( dense optical flow )

refer to this web page
-> http://docs.opencv.org/trunk/doc/py_tutorials/py_video/py_lucas_kanade/py_lucas_kanade.html


dense optical flow is little bit different with feature tracking optical flow.
It search vector flow of all pixels.

In the output flow Mat, included vector point from self current point.
ex) The value of the flow Mat is 30,30 at the position of 20,20. The is directed to the from 20,20 to 30,30

The example source code draws direction of all pixels.
Drawing function is referenced from this site. http://stackoverflow.com/questions/16672003/how-to-extract-velocity-vectors-of-a-pixels-from-calcopticalflowfarneback


This video is result of source code.
Disadvantage is the function is very slow.. gpu version function need. gpu mode source code is here-> http://www.youtube.com/watch?v=tg0oj4ObHlc&feature=youtu.be example soruce code here ->
#include < stdio.h>
#include < iostream>

#include < opencv2\opencv.hpp>
#include < opencv2/core/core.hpp>
#include < opencv2/highgui/highgui.hpp>
#include < opencv2/video/background_segm.hpp>


#ifdef _DEBUG        
#pragma comment(lib, "opencv_core247d.lib")
#pragma comment(lib, "opencv_imgproc247d.lib")   //MAT processing
#pragma comment(lib, "opencv_objdetect247d.lib") //HOGDescriptor
//#pragma comment(lib, "opencv_gpu247d.lib")
//#pragma comment(lib, "opencv_features2d247d.lib")
#pragma comment(lib, "opencv_highgui247d.lib")
#pragma comment(lib, "opencv_ml247d.lib")
//#pragma comment(lib, "opencv_stitching247d.lib");
//#pragma comment(lib, "opencv_nonfree247d.lib");
#pragma comment(lib, "opencv_video247d.lib")
#else
#pragma comment(lib, "opencv_core247.lib")
#pragma comment(lib, "opencv_imgproc247.lib")
#pragma comment(lib, "opencv_objdetect247.lib")
//#pragma comment(lib, "opencv_gpu247.lib")
//#pragma comment(lib, "opencv_features2d247.lib")
#pragma comment(lib, "opencv_highgui247.lib")
#pragma comment(lib, "opencv_ml247.lib")
//#pragma comment(lib, "opencv_stitching247.lib");
//#pragma comment(lib, "opencv_nonfree247.lib");
#pragma comment(lib, "opencv_video247d.lib")
#endif 

using namespace cv;
using namespace std;


void drawOptFlowMap (const Mat& flow, Mat& cflowmap, int step, const Scalar& color) {
 for(int y = 0; y < cflowmap.rows; y += step)
        for(int x = 0; x < cflowmap.cols; x += step)
        {
            const Point2f& fxy = flow.at< Point2f>(y, x);
            line(cflowmap, Point(x,y), Point(cvRound(x+fxy.x), cvRound(y+fxy.y)),
                 color);
            circle(cflowmap, Point(cvRound(x+fxy.x), cvRound(y+fxy.y)), 1, color, -1);
        }
    }


int main()
{
 int s=5;
 //global variables
 Mat GetImg;
 Mat prvs, next; //current frame
 
 char fileName[100] = "mm2.avi"; //video\\mm2.avi"; //mm2.avi"; //cctv 2.mov"; //mm2.avi"; //";//_p1.avi";
 VideoCapture stream1(fileName);   //0 is the id of video device.0 if you have only one camera   

 if(!(stream1.read(GetImg))) //get one frame form video
  return 0;
 resize(GetImg, prvs, Size(GetImg.size().width/s, GetImg.size().height/s) );
 cvtColor(prvs, prvs, CV_BGR2GRAY);

 //unconditional loop   
 while (true) {   
  
  if(!(stream1.read(GetImg))) //get one frame form video   
   break;
  //Resize
  resize(GetImg, next, Size(GetImg.size().width/s, GetImg.size().height/s) );
  cvtColor(next, next, CV_BGR2GRAY);
  ///////////////////////////////////////////////////////////////////
  Mat flow;
  calcOpticalFlowFarneback(prvs, next, flow, 0.5, 3, 15, 3, 5, 1.2, 0);

  Mat cflow;
  cvtColor(prvs, cflow, CV_GRAY2BGR);
  drawOptFlowMap(flow, cflow, 10, CV_RGB(0, 255, 0));
  imshow("OpticalFlowFarneback", cflow);

  ///////////////////////////////////////////////////////////////////
  //Display
  imshow("prvs", prvs);
  imshow("next", next);

  if (waitKey(5) >= 0)   
   break;

  prvs = next.clone();
 }

}



2 comments:

  1. in optical flow why we are using those values like 0.5,2,15,3,1,1.2,0
    please help out

    ReplyDelete
    Replies
    1. These values are known values of the farneback algorithm.
      I used values that people commonly use.
      refer to this url
      http://docs.opencv.org/2.4.7/modules/video/doc/motion_analysis_and_object_tracking.html?highlight=calcopticalflowfarneback#void calcOpticalFlowFarneback(InputArray prev, InputArray next, InputOutputArray flow, double pyr_scale, int levels, int winsize, int iterations, int poly_n, double poly_sigma, int flags)

      Delete