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Editorial Team
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Asked: 2026-06-15T04:24:13+00:00

I have this image : And i want take out the triangle and rectangles

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I have this image:

And i want take out the triangle and rectangles from the image. I have 2 algorithmes, one for triangles and another for rectangles in the code below. But they are very similar. But in this way i only can take out the triangle more bright. Can anyone help me please.

IplImage* DetectAndDrawTriang(IplImage* img){
    CvSeq* contours;
    CvSeq* result;
    CvMemStorage *storage = cvCreateMemStorage(0);
    int d=30;

    IplImage* ret = cvCreateImage(cvGetSize(img), 8, 3);
    IplImage* temp = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
    cvSet(ret,cvScalar(0,0,0));
    cvCvtColor(img, temp, CV_BGR2GRAY);
    cvThreshold( temp, temp, 180, 255, CV_THRESH_BINARY );
    //cvSmooth(temp, temp, CV_GAUSSIAN, 9, 9, 0,0);
    cvNamedWindow("thre");
    cvShowImage("thre", temp);

    cvFindContours(temp, storage, &contours, sizeof(CvContour), CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));

    while(contours)
    {
        result = cvApproxPoly(contours, sizeof(CvContour), storage, CV_POLY_APPROX_DP, cvContourPerimeter(contours)*0.1, 0);
        if(result->total==3)
        {
            CvPoint *pt[3];
            for(int i=0;i<3;i++)
                pt[i] = (CvPoint*)cvGetSeqElem(result, i);


            if((int)sqrt((pt[0]->x-pt[2]->x)*(pt[0]->x-pt[2]->x)+(pt[0]->y-pt[2]->y)*(pt[0]->y-pt[2]->y))>=d && (int)sqrt((pt[0]->x-pt[1]->x)*(pt[0]->x-pt[1]->x)+(pt[0]->y-pt[1]->y)*(pt[0]->y-pt[1]->y))>=d && (int)sqrt((pt[1]->x-pt[2]->x)*(pt[1]->x-pt[2]->x)+(pt[1]->y-pt[2]->y)*(pt[1]->y-pt[2]->y))>=d)
            {
                cvLine(ret, *pt[0], *pt[1], cvScalar(255,255,255));

                cvLine(ret, *pt[1], *pt[2], cvScalar(255,255,255));

                cvLine(ret, *pt[2], *pt[0], cvScalar(255,255,255));
            }
        }
        contours = contours->h_next;
    }

    cvReleaseImage(&temp);
    cvReleaseMemStorage(&storage);

    return ret;

}
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1 Answer

  1. Editorial Team

    One Idea I can think of is using the cv::matchShapes function (I suggest using the cv2 library with Mat instead of Ipl images). matchShapes takes a Mat of the object you want to detect and a Mat of the object you want to compare it against. So in your case you can make a Mat of the contours of a triangle and square and compare those images with each contour in the image your are searching through.

    You may also consider simply doing template matching since your objects are static. Check out cv::matchTemplate and its pretty much the same idea as the above paragraph.

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