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This program demonstrates connected components and use of the trackbar

#include <iostream>
using namespace cv;
using namespace std;
Mat img;
int threshval = 100;
static void on_trackbar(int, void*)
Mat bw = threshval < 128 ? (img < threshval) : (img > threshval);
Mat labelImage(img.size(), CV_32S);
int nLabels = connectedComponents(bw, labelImage, 8);
std::vector<Vec3b> colors(nLabels);
colors[0] = Vec3b(0, 0, 0);//background
for(int label = 1; label < nLabels; ++label){
colors[label] = Vec3b( (rand()&255), (rand()&255), (rand()&255) );
Mat dst(img.size(), CV_8UC3);
for(int r = 0; r < dst.rows; ++r){
for(int c = 0; c < dst.cols; ++c){
int label = labelImage.at<int>(r, c);
Vec3b &pixel = dst.at<Vec3b>(r, c);
pixel = colors[label];
imshow( "Connected Components", dst );
int main( int argc, const char** argv )
CommandLineParser parser(argc, argv, "{@image|stuff.jpg|image for converting to a grayscale}");
parser.about("\nThis program demonstrates connected components and use of the trackbar\n");
cout << "\nThe image is converted to grayscale and displayed, another image has a trackbar\n"
"that controls thresholding and thereby the extracted contours which are drawn in color\n";
String inputImage = parser.get<string>(0);
img = imread(samples::findFile(inputImage), IMREAD_GRAYSCALE);
cout << "Could not read input image file: " << inputImage << endl;
imshow( "Image", img );
namedWindow( "Connected Components", WINDOW_AUTOSIZE);
createTrackbar( "Threshold", "Connected Components", &threshval, 255, on_trackbar );
on_trackbar(threshval, 0);
Designed for command line parsing.
Definition: utility.hpp:818
n-dimensional dense array class
Definition: mat.hpp:811
MatSize size
Definition: mat.hpp:2159
_Tp & at(int i0=0)
Returns a reference to the specified array element.
int cols
Definition: mat.hpp:2137
int rows
the number of rows and columns or (-1, -1) when the matrix has more than 2 dimensions
Definition: mat.hpp:2137
Template class for short numerical vectors, a partial case of Matx.
Definition: matx.hpp:342
std::string String
Definition: cvstd.hpp:152
#define CV_32S
Definition: interface.h:77
#define CV_8UC3
Definition: interface.h:90
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.
int createTrackbar(const String &trackbarname, const String &winname, int *value, int count, TrackbarCallback onChange=0, void *userdata=0)
Creates a trackbar and attaches it to the specified window.
"black box" representation of the file storage associated with a file on disk.
Definition: core.hpp:106
STL namespace.