function showRegions(region_cells, s)
   if (nargin<2)
      s=[];
   end;
   colors={'r','g','b','m','c','y','w','k'}; id = 0;
   for i=1:length(region_cells)
      regions=region_cells{i};
      for j=1:size(regions,2)
         x=regions{3,j}+.5;
         l=line([x(1,:) x(1,1)], [x(2,:) x(2,1)]);
         set(l,'color',colors{mod(id,8)+1});
         if ~isempty(s)
            set(l, s);
         end;
      end;
      id=id+1;
   end;