OpenCV to find specific co-ordinates in an image

Question

I'm working on an iOS app with OpenCV. I am trying to locate the position of the box around the person. I would like to start by getting the width of the box.

I'm converting the image to Greyscale and then using a Canny edge detector.

Link to image here http://s18.postimg.org/bbpczub2x/sampleshot.png

What would be the best way to get the coordinates of the extreme horizontal ends of the box (marked by the red in the picture)? Any pre-existing functions?

are you not using cvRect? Can you use http://opencv.willowgarage.com/documentation/basic_structures.html#cvsize — GPPK, Aug 06 '13 at 10:59
The box is pre-drawn, that is to say before any processing is done. — geekchic, Aug 06 '13 at 11:50

score 1 · Accepted Answer · answered Aug 07 '13 at 07:03

Well I'm going to go ahead and answer this myself. After a bit of digging, I found the Hough Line Transform which perfectly suits my needs.

It is pretty well documented here.

I wanted higher accuracy, so I used HoughLinesP.

    HoughLinesP(dst, lines, 1, CV_PI/180, 100, 100, 10);

The arguments are well defined and its pretty much trial and error after that to perfect it. I've used a Median Blur and a Canny Edge Detector before this for better results.

OpenCV to find specific co-ordinates in an image

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