skeletonization OpenCV in C#

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C#

OpenCV

hi
anyone could give me an example of how to skeletonization without using the transform of the distance, or if you have a skeletonization with the transform of distance running. I have an example with OpenCV in C #, more does not work.
cvlib.CvDistTransform (pimg ref, ref timg, (int) cvlib.CV_DIST_L2, 3, null, null);

An error in the parameters of the null, and I can not solve. if anyone knows how to solve, or some other example please show me.

I am working with OpenCV in C #, but if the example is with OpenCV in C + + or other liguam serves.

thank you