samples/cpp/lkdemo.cpp


An example using the Lucas-Kanade optical flow algorithm

#include <iostream>
#include <ctype.h>
using namespace cv ;
using namespace std ;
static void help()
{
// print a welcome message, and the OpenCV version
cout << "\nThis is a demo of Lukas-Kanade optical flow lkdemo(),\n"
"Using OpenCV version " << CV_VERSION << endl;
cout << "\nIt uses camera by default, but you can provide a path to video as an argument.\n" ;
cout << "\nHot keys: \n"
"\tESC - quit the program\n"
"\tr - auto-initialize tracking\n"
"\tc - delete all the points\n"
"\tn - switch the \"night\" mode on/off\n"
"To add/remove a feature point click it\n" << endl;
}
Point2f point;
bool addRemovePt = false ;
static void onMouse( int event, int x, int y, int /*flags*/ , void * /*param*/ )
{
if ( event == EVENT_LBUTTONDOWN )
{
point = Point2f (( float )x, ( float )y);
addRemovePt = true ;
}
}
int main( int argc, char ** argv )
{
Size subPixWinSize(10,10), winSize(31,31);
const int MAX_COUNT = 500;
bool needToInit = false ;
bool nightMode = false ;
help();
cv::CommandLineParser parser(argc, argv, "{@input|0|}" );
string input = parser. get < string >( "@input" );
if ( input.size() == 1 && isdigit(input[0]) )
cap. open (input[0] - '0' );
else
cap. open (input);
if ( !cap. isOpened () )
{
cout << "Could not initialize capturing...\n" ;
return 0;
}
namedWindow ( "LK Demo" , 1 );
setMouseCallback ( "LK Demo" , onMouse, 0 );
Mat gray, prevGray, image, frame;
vector<Point2f> points[2];
for (;;)
{
cap >> frame;
if ( frame.empty() )
break ;
frame. copyTo (image);
if ( nightMode )
image = Scalar::all (0);
if ( needToInit )
{
// automatic initialization
goodFeaturesToTrack (gray, points[1], MAX_COUNT, 0.01, 10, Mat (), 3, 3, 0, 0.04);
cornerSubPix (gray, points[1], subPixWinSize, Size (-1,-1), termcrit);
addRemovePt = false ;
}
else if ( !points[0].empty() )
{
vector<uchar> status;
vector<float> err;
if (prevGray. empty ())
gray. copyTo (prevGray);
calcOpticalFlowPyrLK (prevGray, gray, points[0], points[1], status, err, winSize,
3, termcrit, 0, 0.001);
size_t i, k;
for ( i = k = 0; i < points[1].size(); i++ )
{
if ( addRemovePt )
{
if ( norm (point - points[1][i]) <= 5 )
{
addRemovePt = false ;
continue ;
}
}
if ( !status[i] )
continue ;
points[1][k++] = points[1][i];
circle ( image, points[1][i], 3, Scalar (0,255,0), -1, 8);
}
points[1].resize(k);
}
if ( addRemovePt && points[1].size() < ( size_t )MAX_COUNT )
{
vector<Point2f> tmp;
tmp.push_back(point);
cornerSubPix ( gray, tmp, winSize, Size (-1,-1), termcrit);
points[1].push_back(tmp[0]);
addRemovePt = false ;
}
needToInit = false ;
imshow ( "LK Demo" , image);
char c = (char) waitKey (10);
if ( c == 27 )
break ;
switch ( c )
{
case 'r' :
needToInit = true ;
break ;
case 'c' :
points[0].clear();
points[1].clear();
break ;
case 'n' :
nightMode = !nightMode;
break ;
}
std::swap (points[1], points[0]);
cv::swap (prevGray, gray);
}
return 0;
}