function mask=dilation(mask,neighboorhood)
%deletion algorithm using 4 pixel neighboors.

%convolve: 

matrix=ones(3,3); 

%4 neighboorhood: 
%corners
if neighboorhood==4,
	matrix(1,1)=0;
	matrix(1,3)=0;
	matrix(3,1)=0;
	matrix(3,3)=0;
end
%center
matrix(2,2)=0;

%convolve mask: 
mask=filter2(matrix,~mask,'same');
pos=find(mask~=0); mask(pos)=1;

%opposite to recover the foreground: 
mask=~mask;