function   [Z,k]=zzlv(X,n)
   X=double(X);
   [M,N]=size(X); 
   Z=zeros(M,N);
  for i=ceil(0.5*n):M-0.5*(n-1)    
     for j=ceil(0.5*n):N-0.5*(n-1)  
         mb=zeros(n,n);
         temp=zeros(n*n);
         k=ceil(n*n*0.5);
         mb=X(i-0.5*(n-1):i+0.5*(n-1),j-0.5*(n-1):j+0.5*(n-1));        
         temp=mb(:);        
       
         for p=1:(length(temp)-1)
            for q=(p+1):(length(temp))
                 if   temp(p)>temp(q) 
                      t=temp(p); 
                      temp(p)=temp(q); 
                      temp(q)=t;
                 end
           end
       end
        s=temp;       
        Z(i,j)=s(k);    
    end
end
Z=uint8(Z)
subplot(122),imshow(Z);
title('after zzlv')