function [max_length] = max_run_length_phi(I, ii,jj, phi)
%
% An auxillary function that computes the run length in the direction phi of an 
% image I starting at the pixel (ii,jj).  That is how many pixels in the direction phi
% match the current pixel value.
%
% Note ii,jj are indexed starting from 1.
%
% max_length = 0 if next pixel is NOT equal to this one (pixel is by 
%            = 1 if we have two of the same pixels in a run
%            = 2 if we have three of the same pixels in a run
% 
% 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 
% 
%-----

[di,dj]    = phi_to_xy_increment(phi);
[M,N]      = size(I);
d          = 1;
ij_value   = I(ii,jj);
max_length = 0;
while( 1 )

  % try to step in the direction phi:
  ii_new = ii+di*d;
  in_I_Range = (ii_new > 0) && (ii_new < M+1);
  if( ~in_I_Range )
    break;
  end
  jj_new = jj+dj*d;
  in_J_Range = (jj_new > 0) && (jj_new < N+1);
  if( ~in_J_Range )
    break;
  end
  if( I(ii_new,jj_new)~=ij_value )
    break;
  end
  
  max_length = max_length + 1;

  d = d+1; % try to step more in the same direction
end