.. _moments: Image Moments ************** Goal ===== In this tutorial you will learn how to: .. container:: enumeratevisibleitemswithsquare * Use the OpenCV function :moments:`moments <>` * Use the OpenCV function :contour_area:`contourArea <>` * Use the OpenCV function :arc_length:`arcLength <>` Theory ====== Code ==== This tutorial code's is shown lines below. You can also download it from `here `_ .. code-block:: cpp #include "opencv2/highgui/highgui.hpp" #include "opencv2/imgproc/imgproc.hpp" #include #include #include using namespace cv; using namespace std; Mat src; Mat src_gray; int thresh = 100; int max_thresh = 255; RNG rng(12345); /// Function header void thresh_callback(int, void* ); /** @function main */ int main( int argc, char** argv ) { /// Load source image and convert it to gray src = imread( argv[1], 1 ); /// Convert image to gray and blur it cvtColor( src, src_gray, CV_BGR2GRAY ); blur( src_gray, src_gray, Size(3,3) ); /// Create Window char* source_window = "Source"; namedWindow( source_window, CV_WINDOW_AUTOSIZE ); imshow( source_window, src ); createTrackbar( " Canny thresh:", "Source", &thresh, max_thresh, thresh_callback ); thresh_callback( 0, 0 ); waitKey(0); return(0); } /** @function thresh_callback */ void thresh_callback(int, void* ) { Mat canny_output; vector > contours; vector hierarchy; /// Detect edges using canny Canny( src_gray, canny_output, thresh, thresh*2, 3 ); /// Find contours findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) ); /// Get the moments vector mu(contours.size() ); for( int i = 0; i < contours.size(); i++ ) { mu[i] = moments( contours[i], false ); } /// Get the mass centers: vector mc( contours.size() ); for( int i = 0; i < contours.size(); i++ ) { mc[i] = Point2f( mu[i].m10/mu[i].m00 , mu[i].m01/mu[i].m00 ); } /// Draw contours Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 ); for( int i = 0; i< contours.size(); i++ ) { Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) ); drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() ); circle( drawing, mc[i], 4, color, -1, 8, 0 ); } /// Show in a window namedWindow( "Contours", CV_WINDOW_AUTOSIZE ); imshow( "Contours", drawing ); /// Calculate the area with the moments 00 and compare with the result of the OpenCV function printf("\t Info: Area and Contour Length \n"); for( int i = 0; i< contours.size(); i++ ) { printf(" * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f \n", i, mu[i].m00, contourArea(contours[i]), arcLength( contours[i], true ) ); Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) ); drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() ); circle( drawing, mc[i], 4, color, -1, 8, 0 ); } } Explanation ============ Result ====== #. Here it is: ========== ========== ========== |MU_0| |MU_1| |MU_2| ========== ========== ========== .. |MU_0| image:: images/Moments_Source_Image.jpg :width: 250pt :align: middle .. |MU_1| image:: images/Moments_Result1.jpg :width: 250pt :align: middle .. |MU_2| image:: images/Moments_Result2.jpg :width: 250pt :align: middle