% C = bord(A,n,m)
% Puts a border of width m (default m=1) around image A
% and gives it value n. If n = NaN: mirror image values.
function C = bord(A,n,m);
if nargin == 2; m=1; end
[x,y] = size(A);
if m > min(x,y)
        mm = min(x,y);
        C = bord(A,n,mm);
        C = bord(C,n,m-mm);
        return
end
if isnan(n)
   C = [A(:,m:-1:1),A,A(:,y:-1:y-m+1)];
   C = [C(m:-1:1,:);C;C(x:-1:x-m+1,:)];
else
   bx = ones(x,m)*n;
   by = ones(m,y+2*m)*n;
   C = [by;[bx,A,bx];by];
end
return