OpenCV  4.5.1
Open Source Computer Vision
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 )
{
VideoCapture cap;
TermCriteria termcrit(TermCriteria::COUNT|TermCriteria::EPS,20,0.03);
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);
cvtColor(image, gray, COLOR_BGR2GRAY);
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;
}
Designed for command line parsing.
Definition: utility.hpp:789
static Scalar_< double > all(double v0)
returns a scalar with all elements set to v0
@ EPS
the desired accuracy or change in parameters at which the iterative algorithm stops
Definition: types.hpp:862
@ COUNT
the maximum number of iterations or elements to compute
Definition: types.hpp:860
#define CV_VERSION
Definition: version.hpp:19
Size2i Size
Definition: types.hpp:347
static double norm(const Matx< _Tp, m, n > &M)
Scalar_< double > Scalar
Definition: types.hpp:669
Point_< float > Point2f
Definition: types.hpp:192
void swap(Mat &a, Mat &b)
Swaps two matrices.
@ EVENT_LBUTTONDOWN
indicates that the left mouse button is pressed.
Definition: highgui.hpp:211
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
int waitKey(int delay=0)
Waits for a pressed key.
void namedWindow(const String &winname, int flags=WINDOW_AUTOSIZE)
Creates a window.
void setMouseCallback(const String &winname, MouseCallback onMouse, void *userdata=0)
Sets mouse handler for the specified window.
void cvtColor(InputArray src, OutputArray dst, int code, int dstCn=0)
Converts an image from one color space to another.
@ COLOR_BGR2GRAY
convert between RGB/BGR and grayscale, color conversions
Definition: imgproc.hpp:546
void circle(InputOutputArray img, Point center, int radius, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a circle.
void goodFeaturesToTrack(InputArray image, OutputArray corners, int maxCorners, double qualityLevel, double minDistance, InputArray mask=noArray(), int blockSize=3, bool useHarrisDetector=false, double k=0.04)
Determines strong corners on an image.
void cornerSubPix(InputArray image, InputOutputArray corners, Size winSize, Size zeroZone, TermCriteria criteria)
Refines the corner locations.
void calcOpticalFlowPyrLK(InputArray prevImg, InputArray nextImg, InputArray prevPts, InputOutputArray nextPts, OutputArray status, OutputArray err, Size winSize=Size(21, 21), int maxLevel=3, TermCriteria criteria=TermCriteria(TermCriteria::COUNT+TermCriteria::EPS, 30, 0.01), int flags=0, double minEigThreshold=1e-4)
Calculates an optical flow for a sparse feature set using the iterative Lucas-Kanade method with pyra...
GOpaque< Size > size(const GMat &src)
Gets dimensions from Mat.
"black box" representation of the file storage associated with a file on disk.
Definition: affine.hpp:52