function B=hitnmiss(A,mask,exten)
% Usage: B=hitnmiss(A,mask,exten)
% hit and miss transform with 3 x 3 mask
% to handle don't care, convert binary image into +1, -1 image
% don't care entries are represented with 0.
% A: binary matrix
% mask: +1, -1 and 0 for don't care
% B: binary output matrix, same size as A
% exten (default = 1): Outside the boundary of A, it is assumed 
%   by default, they are all -1s (0 extension). Don't care
%   extension has not been implemented yet.
% 
% (C) 2003 by Yu Hen Hu
% created: 12/1/2003

exten=1; % default extension. Other choices may be implemented in the 
         % future.

[ms,ns]=size(mask);
if ms~=3 | ns~=3, error('mask size must be 3 x 3'),end
thresh=sum(sum(abs(mask))); % number of elements that must be matched

[m,n]=size(A); 
A=2*A-ones(m,n);
m1=rem(m,3); if m1~=0, m1=3-m1; end
n1=rem(n,3); if n1~=0, n1=3-n1; end
      
Aa=[-exten*ones(m+m1+2,1) [-exten*ones(1,n);A;-exten*ones(m1+1,n)] ...
    -exten*ones(m+m1+2,n1+1)]; % border is 0 extension by default
[ma,na]=size(Aa);
m2=floor(ma/3); n2= floor(na/3);
% mask 1: foreground, -1: background, 0: don't care
% 
bigmask=kron(ones(m2,n2),mask);
[m3,n3]=size(bigmask);

Ahm=zeros(m+m1,n+n1);
for i=1:3,
   for j=1:3,
      tmp=bigmask.*Aa(i:m3+i-1,j:n3+j-1);
      tmp1=blkproc(tmp,[3 3],'sum(sum(x))');
      Ahm([1:3:m]+i-1,[1:3:n]+j-1)=[tmp1==thresh];
   end
end
B=Ahm([1:m],[1:n]);