How could I make the discontinuous contour of an image consistant?

Question

In the task, I got an discontinuous edge image, how could make it closed? in other word make the curve continuous. And the shape could be any kind, cause this the coutour shadow

Answer 1

Here's another suggestion that is more "computer vision literature" oriented.

As a rule of thumb preprocessing step, it is usually a good idea to thin all the edges to make sure they are about 1 pixel thick. A popular edge thinning method is non-maximal suppression (NMS).

Then I would start off by analyzing the image, and finding all the connected components that I have. OpenCV already provides the connectedComponents function. Once groups of connected components are determined, you can fit a Bezier curve to each group. An automatic method of fitting Bezier curves to a set of 2D points is available in the Graphics Gem book. There's also C code available for their method. The goal of fitting a Bezier curve is to get as much high-level understanding of each component group as possible.

Next, you need to join those Bezier curves together. A method of joining lines using endpoints clustering is available in the work of Shpitalni and Lipson. In that paper, take a look at their adaptive clustering method in the section named "Entity Linking and Endpoint Clustering".

Finally, with all the curves grouped together you can fit a final Bezier curve too all the points that you have to get a nice and natural looking edge map.

As a side note, you can take a look at the work Ming-Ming Cheng in cartoon curve extraction. There's OpenCV-based code available for that method here too, but will output the following once applied to your image:

Disclaimer:
I can attest to the performance of the Bezier curve fitting algorithm as I've personally used it and it works pretty well. Cheng's curve extraction algorithm works well too, however, it will create bad looking "blobs" with thin contours due to the use of gradient detection (which has a tendency of making thin lines thick!). If you could find a way to work around this "thickening" effect, you can skip Bezier curve extraction and jump right into endpoint clustering to join the curves together.

Hope this helps!