How does one fill a closed contour?

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Jose Dolz

Hi He,

there are a lot of image processing libraries for C++ that includes the option to fill a given contours. If you are using 2D images I would suggest to use openCV. However, if you are using 3D images, ITK is a good choice.

Cheers.

He Sheng

Hi Jose,

Thanks for your answer. The question is that I do not want to use third-party libraries, like OpenCV or Matlab. I try to find some algorithms to do it efficiently.

Thanks for your answer.

Girish Mallya Udupi

To fill a closed contour, you will need to

(1) Find a point which is inside the contour. This would be your seed point.

(2) Use a seed-fill algorithm. i.e., fill the 8-/4-connected area of the seed point. "imfill" in MATLAB does that.

Both (1) and (2) can easily be achieved using OpenCV functions. But I understand from your comment that you want to implement them from scratch.

For (1), check out http://en.wikipedia.org/wiki/Point_in_polygon (Peter has already mentioned one of the algorithms for this problem).

For (2), check out http://en.wikipedia.org/wiki/Flood_fill.

Lambert Zijp

To circumvent the seed(s) problem, you could do a reverse floodfill: assume the pixel in e.g. the upper-left corner is outside, use that corner as a seed for floodfill, and XOR the result.

Floodfill can be done recursively with an advancing front queue.