draw a line arounde black shapes in C#

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C#

C#4.0

hi guys .
i succeeded to seprate shapes with specific color (black) in image ...
i used EuclideanColorFiltering in my project .
here this is my code :

EuclideanColorFiltering filter = new EuclideanColorFiltering();

Bitmap CopyImage = null;
          filter.CenterColor = new RGB(0, 0, 0);
          filter.FillColor = new RGB(169, 169, 169);
          filter.Radius = 150;
          CopyImage = image;
          // apply the filter
          filter.ApplyInPlace(CopyImage);

it works ok
now i want to draw a green line around of the black shapes ,,,
how can i do this ?