Closing a contour curve in OpenCV

Question

I'm using OpenCV (Canny + findCountours) to find external contours of objects. The curve drawn is typically almost, but not entirely, closed. I'd like to close it - to find the region it bounds.

How do I do this?

Things considered:

Dilation - the examples I've seen show this after Canny, although it would seem to me it makes more sense to do this after findContours
Convex hull - might work, though I'm really trying to complete a curve
Shape simplification - related, but not exactly what I want

Just duplicate the first element of the contour list at the end? — Martin Beckett
– Martin Beckett, Commented Jan 31, 2014 at 0:08
MartinBeckett, berak, I think both comments should have been answers, +1 for both — Abid Rahman K
– Abid Rahman K, Commented Jan 31, 2014 at 8:20

Muhammad Abdullah · Accepted Answer · 2017-08-15 09:04:47Z

1

Using PolyLine method to draw contours

cv2.PolyLine(img, points, is_closed=True, 255, thickness=1, lineType=8, shift=0)

Read the docs for further details: http://docs.opencv.org/2.4/modules/core/doc/drawing_functions.html

Mark answered if it resolved your problem. If not then let me know.

answered Aug 15, 2017 at 9:04

Muhammad Abdullah

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The man they call Jayne · Accepted Answer · 2017-07-26 01:09:53Z

0

A little late, but I just had to deal with this myself. If you perform an opening operation (erosion followed by dilation) prior to the Canny edge detection, the edges you detect should be more continuous, resulting in better contours. This method appears to be fairly robust. I mentioned this in another post and posted a code sample as part of a recent question.

answered Jul 26, 2017 at 1:09

The man they call Jayne

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