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how to find the coordinate of top/bottom/left and right points

asked 2013-12-09 06:39:08 -0500

ati gravatar image

updated 2016-01-22 07:03:52 -0500

how do I find the coordinate of these 4 points in a detected object(which does not have any specific shape)? image description

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answered 2013-12-09 06:52:31 -0500

Haris gravatar image

updated 2013-12-09 07:18:43 -0500

You can follow below method to achieve this.

  • Segment the four dotted region. Use inRange to segment the dots, better to convert to HSV color space before inRange.
  • Use OpenCV Find contour get the contour in image.
  • Use OpenCV moments to find the centre point of your contour


    #include <iostream>
    #include "opencv2/opencv.hpp"
    #include <stdio.h>     
    using namespace std;
    using namespace cv;
    int main( int argc, char** argv )
        Mat src=imread("img.png",1);
        Mat hsv,thr;
       // inRange(hsv,Scalar(160,0,120), Scalar(179,255,200), thr);
        inRange(src,Scalar(20,0,120), Scalar(25,0,200), thr);        
       vector<vector<Point> > contours;
       vector<Vec4i> hierarchy;
       findContours( thr, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
      /// Get the moments
      vector<Moments> mu(contours.size() );
      for( int i = 0; i < contours.size(); i++ )
         { mu[i] = moments( contours[i], false ); }
      ///  Get the mass centers:
      vector<Point2f> 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
      for( int i = 0; i< contours.size(); i++ )
           circle( src, mc[i], 10, Scalar(0,0,255), 1,CV_AA, 0 );
    waitKey(); }


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answered 2014-10-07 11:43:03 -0500

Pauie gravatar image

what if there are no dots how to find the extreme points of an object in an image? topmost, leftmost, rightmost, bottom

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Then you should create a black-white mask of your retrieved object. Loop over the image, at each white pixel, see if the current pixel has a value that is better then a previous found candidate for topmost leftmost rightmost or bottom pixel. If so replace.

StevenPuttemans gravatar imageStevenPuttemans ( 2014-10-08 04:24:03 -0500 )edit

Or use contour approach like, find contour->bounding box for contour etc...See the tutorial here

Haris gravatar imageHaris ( 2014-10-08 07:26:22 -0500 )edit

This is of great help

oyashi gravatar imageoyashi ( 2015-03-30 17:38:25 -0500 )edit
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Asked: 2013-12-09 06:39:08 -0500

Seen: 9,117 times

Last updated: Oct 07 '14