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POHow to use convexityDefects in Opencv 2.4
 

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  1. POHow to use convexityDefects in Opencv 2.4
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    <p>I try to use <code>convexHull</code> and <code>convexityDefects</code> to define a hand. But when the program hit the <code>convexityDefects</code>, there is always an error says "vector subscript out of range". here is my code.</p> <p>Did I use the function in a wrong way? </p> <pre><code>#include "stdafx.h" #include &lt;opencv2\opencv.hpp&gt; #include &lt;math.h&gt; #include &lt;iostream&gt; using namespace cv; using namespace std; const int w = 500; int levels = 3; vector&lt;vector&lt;Point&gt; &gt; contours; vector&lt;Vec4i&gt; hierarchy; void on_trackbar(int, void*) { Mat cnt_img = Mat::zeros(w, w, CV_8UC3); int _levels = levels - 3; drawContours( cnt_img, contours, _levels &lt;= 0 ? 3 : -1, Scalar(128,255,255), 3, CV_AA, hierarchy, std::abs(_levels) ); imshow("contours", cnt_img); } int main( int argc, char**) { Mat img = imread("out.jpg",0); threshold(img,img,200,255,cv::THRESH_BINARY); namedWindow( "image", 1 ); imshow( "image", img ); //Extract the contours so that vector&lt;vector&lt;Point&gt; &gt; contours0; findContours( img, contours0, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE); contours.resize(contours0.size()); for( size_t k = 0; k &lt; contours0.size(); k++ ){ std::cout&lt;&lt;"contours0.size"&lt;&lt;contours0[k].size()&lt;&lt;endl; approxPolyDP(Mat(contours0[k]), contours[k], 0, true); } std::vector&lt;Vec4i&gt; defects; vector&lt;cv::vector&lt;int&gt; &gt;hull( contours.size() ); for (int i = 0; i &lt; contours.size(); i++) { std::cout&lt;&lt;"contours.size"&lt;&lt;contours[i].size()&lt;&lt;endl; convexHull( contours[i], hull[i], false ); if (contours[i].size() &gt;150 ) { convexityDefects(contours[i], hull[i], defects[i]); std::cout&lt;&lt;"defects"&lt;&lt;defects[i].depth&lt;&lt;endl; } } namedWindow( "contours", 1 ); createTrackbar( "levels+3", "contours", &amp;levels, 7, on_trackbar ); on_trackbar(0,0); waitKey(); return 0; } </code></pre> <p>Thank you in advance!</p>
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    1. USJane Wang
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