Calculate the center of a contour/Area

Question

I'm working on a Image-processing chain that seperates a single object by color and contour and then calculates the y-position of this object.

How do I calculate the center of a contour or area with OpenCV?

Opencv links:

• http://opencv.willowgarage.com/wiki/
• http://en.wikipedia.org/wiki/OpenCV

Answer 1

You can get the center of mass in the y direction by first calculating the Moments. Then the center of mass is given by yc = M01 / M00, where M01 and M00 are fields in the structure returned by the Moments call.

If you just want the center of the bounding rectangle, that is also easy to do with BoundingRect. This returns you a CvRect and you can just take half of the height.

Let me know if this isn't precise enough, I have sample code somewhere I can dig up for you.

Answer 2

I don't exactly know what OpenCV is, but I would suggest this:

The Selected cluster of pixels has a maximum width at one point - w - so lets say the area has w vertical columns of pixels. Now I would weight the columns according to how many pixels the column contains, and use these column-wights to determine the Horizontal Center Point.

The Same Algorithm could also work for the X Center.