example_14-03.cpp

// Example 14-3. Drawing labeled connected components

#include <algorithm>
#include <iostream>
#include<opencv2/opencv.hpp>

using namespace std;

int main(int argc, char* argv[]) {

  cv::Mat img, img_edge, labels, img_color, stats;

  // load image or show help if no image was provided
  if( argc != 2
  || (img = cv::imread( argv[1], cv::IMREAD_GRAYSCALE )).empty()
  ) {
    cout << "\nExample 8_3 Drawing Connected componnents\n" \
    << "Call is:\n" <<argv[0] <<" image\n\n";
    return -1;
  }

  cv::threshold(img, img_edge, 128, 255, cv::THRESH_BINARY);
  cv::imshow("Image after threshold", img_edge);

  int i, nccomps = cv::connectedComponentsWithStats (
  img_edge, labels,
  stats, cv::noArray()
  );
  cout << "Total Connected Components Detected: " << nccomps << endl;

  vector<cv::Vec3b> colors(nccomps+1);
  colors[0] = cv::Vec3b(0,0,0); // background pixels remain black.
  for( i = 1; i <= nccomps; i++ ) {
    colors[i] = cv::Vec3b(rand()%256, rand()%256, rand()%256);
    if( stats.at<int>(i-1, cv::CC_STAT_AREA) < 100 )
    colors[i] = cv::Vec3b(0,0,0); // small regions are painted with black too.
  }
  img_color = cv::Mat::zeros(img.size(), CV_8UC3);
  for( int y = 0; y < img_color.rows; y++ )
    for( int x = 0; x < img_color.cols; x++ )
    {
      int label = labels.at<int>(y, x);
      CV_Assert(0 <= label && label <= nccomps);
      img_color.at<cv::Vec3b>(y, x) = colors[label];
    }

  cv::imshow("Labeled map", img_color);
  cv::waitKey();
  return 0;
}