active contours for a specific image

Hello,
I have this image in input : http://sylvain-ard.fr/temp/CONTOURS_LEAFLET1.jpg
a leaf so
and I want to apply this algorithm : https://itk.org/ITKExamples/src/Segmentation/LevelSets/SegmentWithGeodesicActiveContourLevelSet/Documentation.html
to close and fill the contour
I see that I should use a negative propagation scaling but I don’t know what to do exactly.
Could you help me please ?
Thank you.
Best regards

up please