connectedComponents: warning free version

modules/imgproc/include/opencv2/imgproc/imgproc.hpp

@@ -1091,6 +1091,11 @@ enum { TM_SQDIFF=0, TM_SQDIFF_NORMED=1, TM_CCORR=2, TM_CCORR_NORMED=3, TM_CCOEFF
 CV_EXPORTS_W void matchTemplate( InputArray image, InputArray templ,
                                  OutputArray result, int method );
 
+//! computes the connected components labeled image of boolean image I with 4 or 8 way connectivity - returns N, the total
+//number of labels [0, N-1] where 0 represents the background label.
+CV_EXPORTS_W uint64_t connectedComponents(Mat &L, const Mat &I, int connectivity = 8);
+
+
 //! mode of the contour retrieval algorithm
 enum
 {

samples/cpp/connected_components.cpp

@@ -11,25 +11,21 @@ int threshval = 100;
 static void on_trackbar(int, void*)
 {
     Mat bw = threshval < 128 ? (img < threshval) : (img > threshval);
-
-    vector<vector<Point> > contours;
-    vector<Vec4i> hierarchy;
-
-    findContours( bw, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );
-
-    Mat dst = Mat::zeros(img.size(), CV_8UC3);
-
-    if( !contours.empty() && !hierarchy.empty() )
-    {
-        // iterate through all the top-level contours,
-        // draw each connected component with its own random color
-        int idx = 0;
-        for( ; idx >= 0; idx = hierarchy[idx][0] )
-        {
-            Scalar color( (rand()&255), (rand()&255), (rand()&255) );
-            drawContours( dst, contours, idx, color, CV_FILLED, 8, hierarchy );
-        }
+    Mat labelImage(img.size(), CV_32S);
+    int nLabels = connectedComponents(labelImage, bw, 8);
+    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 );
 }