makelut.m

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function lut = makelut(varargin)
%MAKELUT Construct lookup table for use with APPLYLUT.
%   LUT = MAKELUT(FUN,N) returns a lookup table for use with
%   APPLYLUT.  FUN is either a string containing the name of a
%   function or an inline function object.  The function should
%   take a 2-by-2 or 3-by-3 matrix of 1's and 0's as input and
%   return a scalar.  N is either 2 or 3, indicating the size of
%   the input to FUN.  MAKELUT creates LUT by passing all
%   possible 2-by-2 or 3-by-3 neighborhoods to FUN, one at a
%   time, and constructing either a 16-element vector (for 2-by-2
%   neighborhoods) or a 512-element vector (for 3-by-3
%   neighborhoods).  The vector consists of the output from FUN
%   for each possible neighborhood.
%
%   LUT = MAKELUT(FUN,N,P1,P2,...) passes the additional
%   parameters P1, P2, ..., to FUN.
%
%   Class Support
%   -------------
%   LUT is returned as a vector of class double.
%
%   Example
%   -------
%       f = inline('sum(x(:)) >= 2');
%       lut = makelut(f,2);
%
%   See also APPLYLUT.

%   Steven L. Eddins, March 1996
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 1.10 $  $Date: 1997/11/24 15:35:51 $

if (nargin < 2)
    error('Too few input arguments');
end

fun = varargin{1};
n = varargin{2};
params = varargin(3:end);
fun = fcnchk(fun, length(params));

if (n == 2)
    lut = zeros(16,1);
    for k = 1:16
        a = reshape(fliplr(dec2bin(k-1,4) == '1'), 2, 2);
        lut(k) = feval(fun, a, params{:});
    end
    
elseif (n == 3)
    lut = zeros(512,1);
    for k = 1:512
        a = reshape(fliplr(dec2bin(k-1,9) == '1'), 3, 3);
        lut(k) = feval(fun, a, params{:});
    end
    
else
    error('N must be 2 or 3');

end