2017-08-24 16:25:27 -0500 received badge ● Student (source) 2015-12-21 04:23:34 -0500 commented answer not rect ROI defined by 4 points This solution works fine, but I have to store points after convexhull in a different vector. Adding: cerr << "A " << points.at(0).x << " - " << points.at(0).y << endl; cerr << "B " << points.at(1).x << " - " << points.at(1).y << endl; cerr << "C " << points.at(2).x << " - " << points.at(2).y << endl; cerr << "D " << points.at(3).x << " - " << points.at(3).y << endl;  Before and after convexhull i have: A 300 - 50 B 300 - 20 C 150 - 300 D 200 - 300 A 300 - 50 B 200 - 300 C 150 - 300 D 200 - 300 And the point (300,20) disappear. With:  vector points2; //Find the corresponding ROI based on the poitns convexHull(points, points2); //to assure correct point order  It all works fine! Thank you 2015-12-21 04:18:56 -0500 received badge ● Supporter (source) 2015-12-21 02:54:10 -0500 commented answer not rect ROI defined by 4 points I don't need the number of pixel of one color. The image is thresholded and is black and white. I need to know how many white pixel there are only in the ROI, non in the complete image. 2015-12-20 17:13:58 -0500 received badge ● Editor (source) 2015-12-20 12:56:24 -0500 asked a question not rect ROI defined by 4 points Hi, I would use the method countNonZero (InputArray src) on a ROI of my image; The ROI is not a rect, but it's defined by the points A, B, C, D like the red zone in the figure. How can I use this method on this ROI? 2015-11-11 12:45:27 -0500 received badge ● Enthusiast 2015-11-09 09:37:22 -0500 commented question ear classifier for frontal face I didn't do it! 2015-11-09 09:29:39 -0500 received badge ● Scholar (source) 2015-11-09 06:06:57 -0500 asked a question BackgroundSubtractorMOG2 set parameters Hi, i'm trying to use the class BackgroundSubtracorMOG2 with Opencv 3.0. After: Ptr pMOG2; pMOG2 = createBackgroundSubtractorMOG2();  I want to set some parameters like:  pMOG2.setShadowThreshold(0.5);  But it tells me: No member named 'setShadowThreshold' in 'cv::Ptr' Same with the operator "->" instead of "." Do you know how to set parameters of this class? 2015-01-26 10:48:52 -0500 asked a question ear classifier for frontal face Hi all, I need an ears detector from frontal face image. haarcascade_mcs_leftear.xml in openCV/data/haarcascade works only with profile image and not with frontal faces. Do you know how can I solve this problem? Thanks Giuseppe