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POHow to find corner coordinates of Image contour in Opencv and C
 

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  1. POHow to find corner coordinates of Image contour in Opencv and C
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    <p>I have to find corner points of an image so that I can crop it in rectangular shape.I have already found the contour and used approxpoly() function on it.Now how to find the corner Co-ordinates of the contour ? Here is my C code-></p> <pre><code>#include &lt;cv.h&gt; #include &lt;highgui.h&gt; int main(int argc, char** argv) { IplImage *img,*gray; if((img = cvLoadImage("save.jpg", 1)) == NULL) { printf("A Img open error\n"); } gray=cvCreateImage( cvGetSize(img), IPL_DEPTH_8U, 1 ); cvCvtColor(img,gray,CV_BGR2GRAY); IplImage* out_median = cvCreateImage(cvGetSize(gray),IPL_DEPTH_8U,1); cvSmooth( gray,out_median,CV_MEDIAN,3); IplImage* out_threshold = cvCreateImage( cvGetSize(out_median), out_median-&gt;depth, 1); cvThreshold(out_median,out_threshold,1,255,CV_THRESH_BINARY); CvMemStorage* storage = cvCreateMemStorage(); CvSeq* first_contour = NULL; cvFindContours(out_threshold,storage,&amp;first_contour,sizeof(CvContour),CV_RETR_LIST,CV_CHAIN_APPROX_SIMPLE); CvSeq* approx_polygon = NULL; approx_polygon=cvApproxPoly(first_contour,sizeof(CvContour),storage,CV_POLY_APPROX_DP,0.01*cvArcLength(first_contour,CV_WHOLE_SEQ, 1),0); //cvDrawContours(out_threshold,approx_polygon,cvScalarAll(255),cvScalarAll(255),100); //cvShowImage("Contours", out_threshold ); //cvSaveImage("save_approxpoly_contour.jpg",out_threshold); cvWaitKey(0); return 0; </code></pre> <p>}</p> <p>This my Contour Image after applying the Approxpoly() <img src="https://i.stack.imgur.com/DGGxX.jpg" alt="enter image description here"></p>
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    1. COIf you already have the contours, a simple math calc would reveal the points of the corner. Do a simple iteration on the points you have, looking for the top-left, top-right, bottom-left and bottom-right points. There's no need to use an additional library for this. This is basic math calc, if I understood your problem right.
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      1. USkarlphillip
    2. COyea I know what you are talking about ,like for finding the bottom-rightmost coordinate of the contour ,the product should be maximum. Can you tell me what function will give me the points so that can iterate them.Is there anything like contour->x/y or something like that to get the points.
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      1. USdeepak_k
    3. COhttp://tech.dir.groups.yahoo.com/group/OpenCV/message/51631
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      1. USAbid Rahman K
 

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