function [asm] = ASM(I, d,phi)
% 
% Written by:
% -- 
% John L. Weatherwax                2005-08-04
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
% Epage 
% 
%-----

if( nargin>1 ) % compute the ASM for just one displacement and angular direction

  P   = co_occurrence(I, d,phi);
  P2  = P.^2;
  asm = sum(P2(:));
  
else % compute the CON for all angles and average 
  
  d = 1; % assume d=1

  all_phis = [ 0, 45, 90, 135 ];
  all_asms = zeros(1,length(all_phis));
  for ii=1:length(all_phis)
    
    a = ASM(I, d,all_phis(ii)); % recursively call the three argument case  
    all_asms(ii) = a;
    
  end
  
  asm = mean(all_asms);
  
end