How to Close an Open Contour

Dear all, Attached image consists of two open contours. I would like to close these two contours. Please let me know if this is doable in Matlab.

Thanks Ashkan

Answer 1

[Image Analyst]

Skeletonize the blob with bwmorph(), then use bwmorph() again to find the endpoints. Use regionprops() to get coordinates of the skeleton so you know which endpoints belong to the same blob. Then use imline() to draw a line connecting the endpoints of each blob. Demo of imline used to burn a line into an image is attached. Please try these steps yourself first and come back with your code if you can't do it. Again, the rough steps are

bwmorph(binaryImage, 'skel', inf);
bwmorph(binaryImage, 'endpoints');
[labeledImage, numBlobs] = bwlabel(binaryImage);
measurements = regionprops(labeledImage, 'PixelList');
for k = 1 : numBlobs
    % find endpoints of this blob, then
    imline();
    % etc
end

Finish it up (it shouldn't be too hard) and let me know of any problems.

[Ashkan Javadzadegan]

Thanks for this. I ran the first four lines, up to "for" loop, and it returned four end points. However, the loop requires clicking by user to close the contours, but I need it to be done automatically without clicking. I attach herewith my source code and input image. I would be very grateful if you would have a look and let me know.

[Paul Simon]

I'm in a similiar situation. Did you manage to solve it?

[Stelios Fanourakis]

I do have similar situation. Did you manage to find a solution?

[Image Analyst]

Didn't I outline the solution : use imline() to join the endpoints of each skeleton. Can't you find the endpoints of each blob? Hint: use ismember() or a for loop to find out which endpoints belong to regionprops(k).PixelList().

[darova]

i accepted the answer

Answer 2

[Daniel Thomas]

Don't "burn lines" with imline. Use insertShape instead to draw a line on an image. Additional trouble with insertShape is that it always produces RGB instead of grayscale. So you need to convert it to grayscale. Other than that, it works a lot better than "burning the lines."

[Image Analyst]

It also requires the Computer Vision Toolbox.