i = ;

b=DeleteSmallComponents@FillingTransform@ChanVeseBinarize[i,"TargetColor"->Red];
skeleton=SkeletonTransform[b];
pruned=Pruning[skeleton,1,5];
mask=InverseDistanceTransform[pruned];
res=SetAlphaChannel[i,mask];
Grid[{{i,b,skeleton},{pruned,mask,res}}]