let se = if useOctagon
then (octagon (2 * r - 1)).Mat // It doesn't speed up the process.
else CvInvoke.GetStructuringElement(CvEnum.ElementShape.Ellipse, Size(2 * r, 2 * r), Point(-1, -1))
let se = if useOctagon
then (octagon (2 * r - 1)).Mat // It doesn't speed up the process.
else CvInvoke.GetStructuringElement(CvEnum.ElementShape.Ellipse, Size(2 * r, 2 * r), Point(-1, -1))