OpenCV  4.5.2
Open Source Computer Vision
samples/cpp/segment_objects.cpp

An example using drawContours to clean up a background segmentation result

#include <stdio.h>
#include <string>
using namespace std;
using namespace cv;
static void help(char** argv)
{
printf("\n"
"This program demonstrated a simple method of connected components clean up of background subtraction\n"
"When the program starts, it begins learning the background.\n"
"You can toggle background learning on and off by hitting the space bar.\n"
"Call\n"
"%s [video file, else it reads camera 0]\n\n", argv[0]);
}
static void refineSegments(const Mat& img, Mat& mask, Mat& dst)
{
int niters = 3;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
Mat temp;
dilate(mask, temp, Mat(), Point(-1,-1), niters);
erode(temp, temp, Mat(), Point(-1,-1), niters*2);
dilate(temp, temp, Mat(), Point(-1,-1), niters);
findContours( temp, contours, hierarchy, RETR_CCOMP, CHAIN_APPROX_SIMPLE );
dst = Mat::zeros(img.size(), CV_8UC3);
if( contours.size() == 0 )
return;
// iterate through all the top-level contours,
// draw each connected component with its own random color
int idx = 0, largestComp = 0;
double maxArea = 0;
for( ; idx >= 0; idx = hierarchy[idx][0] )
{
const vector<Point>& c = contours[idx];
double area = fabs(contourArea(Mat(c)));
if( area > maxArea )
{
maxArea = area;
largestComp = idx;
}
}
Scalar color( 0, 0, 255 );
drawContours( dst, contours, largestComp, color, FILLED, LINE_8, hierarchy );
}
int main(int argc, char** argv)
{
VideoCapture cap;
bool update_bg_model = true;
CommandLineParser parser(argc, argv, "{help h||}{@input||}");
if (parser.has("help"))
{
help(argv);
return 0;
}
string input = parser.get<std::string>("@input");
if (input.empty())
cap.open(0);
else
cap.open(samples::findFileOrKeep(input));
if( !cap.isOpened() )
{
printf("\nCan not open camera or video file\n");
return -1;
}
Mat tmp_frame, bgmask, out_frame;
cap >> tmp_frame;
if(tmp_frame.empty())
{
printf("can not read data from the video source\n");
return -1;
}
namedWindow("video", 1);
namedWindow("segmented", 1);
Ptr<BackgroundSubtractorMOG2> bgsubtractor=createBackgroundSubtractorMOG2();
bgsubtractor->setVarThreshold(10);
for(;;)
{
cap >> tmp_frame;
if( tmp_frame.empty() )
break;
bgsubtractor->apply(tmp_frame, bgmask, update_bg_model ? -1 : 0);
refineSegments(tmp_frame, bgmask, out_frame);
imshow("video", tmp_frame);
imshow("segmented", out_frame);
char keycode = (char)waitKey(30);
if( keycode == 27 )
break;
if( keycode == ' ' )
{
update_bg_model = !update_bg_model;
printf("Learn background is in state = %d\n",update_bg_model);
}
}
return 0;
}
Point2i Point
Definition: types.hpp:194
Scalar_< double > Scalar
Definition: types.hpp:669
#define CV_8UC3
Definition: interface.h:90
cv::String findFileOrKeep(const cv::String &relative_path, bool silentMode=false)
Definition: utility.hpp:1167
GMat mask(const GMat &src, const GMat &mask)
Applies a mask to a matrix.
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 drawContours(InputOutputArray image, InputArrayOfArrays contours, int contourIdx, const Scalar &color, int thickness=1, int lineType=LINE_8, InputArray hierarchy=noArray(), int maxLevel=INT_MAX, Point offset=Point())
Draws contours outlines or filled contours.
@ LINE_8
8-connected line
Definition: imgproc.hpp:815
@ FILLED
Definition: imgproc.hpp:813
void dilate(InputArray src, OutputArray dst, InputArray kernel, Point anchor=Point(-1,-1), int iterations=1, int borderType=BORDER_CONSTANT, const Scalar &borderValue=morphologyDefaultBorderValue())
Dilates an image by using a specific structuring element.
void erode(InputArray src, OutputArray dst, InputArray kernel, Point anchor=Point(-1,-1), int iterations=1, int borderType=BORDER_CONSTANT, const Scalar &borderValue=morphologyDefaultBorderValue())
Erodes an image by using a specific structuring element.
double contourArea(InputArray contour, bool oriented=false)
Calculates a contour area.
void findContours(InputArray image, OutputArrayOfArrays contours, OutputArray hierarchy, int mode, int method, Point offset=Point())
Finds contours in a binary image.
@ CHAIN_APPROX_SIMPLE
Definition: imgproc.hpp:442
@ RETR_CCOMP
Definition: imgproc.hpp:428
Ptr< BackgroundSubtractorMOG2 > createBackgroundSubtractorMOG2(int history=500, double varThreshold=16, bool detectShadows=true)
Creates MOG2 Background Subtractor.
"black box" representation of the file storage associated with a file on disk.
Definition: affine.hpp:52