nlfilter.m

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function b = nlfilter(varargin)
%NLFILTER Perform general sliding-neighborhood operations.
%   B = NLFILTER(A,[M N],FUN) applies the function FUN to
%   each M-by-N sliding block of A.  FUN may be a string
%   containing the name of a function, a string containing an
%   expression, or an inline function object.  FUN should accept
%   an M-by-N block as input, and return a scalar result:
%
%       C = FUN(X)
%
%   C is the output value for the center pixel in the M-by-N
%   block X. NLFILTER calls FUN for each pixel in A. NLFILTER
%   zero pads the M-by-N block at the edges, if necessary.
%
%   B = NLFILTER(A,[M N],FUN,P1,P2,...) passes the additional
%   parameters P1,P2,..., to FUN.
%
%   B = NLFILTER(A,'indexed') processes A as an indexed image,
%   padding with ones if A is of class double and zeros if A is
%   of class uint8.
%
%   Class Support
%   -------------
%   The input image A can be of any class supported by FUN. The
%   class of B depends on the class of the output from FUN.
%
%   Remarks
%   -------
%   NLFILTER can take a long time to process large images. In
%   some cases, the COLFILT function can perform the same
%   operation much faster.
%
%   Example
%   -------
%   This call produces the same result as calling MEDFILT2 with a
%   3-by-3 neighborhood:
%
%       B = NLFILTER(A,[3 3],'median(x(:))');
%
%   See also BLKPROC, COLFILT.

%   Clay M. Thompson 1-25-93
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 5.11 $  $Date: 1997/11/24 15:35:59 $

[a, nhood, fun, params, padval] = parse_inputs(varargin{:});

% Expand A
[ma,na] = size(a);
if (isa(a,'uint8'))
    % padval should always be 0 for uint8 inputs
    aa = repmat(uint8(0),size(a)+nhood-1);
else
    if (padval == 1)
        aa = ones(size(a)+nhood-1);
    else
        aa = zeros(size(a)+nhood-1);
    end
end
aa(floor((nhood(1)-1)/2)+[1:ma],floor((nhood(2)-1)/2)+[1:na]) = a;

% Find out what output type to make.
rows = [0:nhood(1)-1]; cols = [0:nhood(2)-1];
if (isa(feval(fun,aa(1+rows,1+cols),params{:}), 'uint8'))
    b = repmat(uint8(0), size(a));
else
    b = zeros(size(a));
end
    
% Apply m-file to each neighborhood of a
f = waitbar(0,'Applying neighborhood operation...');
for i=1:ma,
  for j=1:na,
    x = aa(i+rows,j+cols);
    b(i,j) = feval(fun,x,params{:});
  end
  waitbar(i/na)
end
close(f)

%%%
%%% Function parse_inputs
%%%
function [a, nhood, fun, params, padval] = parse_inputs(varargin)

switch nargin
case 0
    error('Too few inputs to NLFILTER');
case 1
    error('Too few inputs to NLFILTER');
case 2
    error('Too few inputs to NLFILTER');
case 3
    if (strcmp(varargin{2},'indexed'))
        error('Too few inputs to NLFILTER');
    else
        % NLFILTER(A, [M N], 'fun')
        a = varargin{1};
        nhood = varargin{2};
        fun = varargin{3};
        params = cell(0,0);
        padval = 0;
    end
    
otherwise
    if (strcmp(varargin{2},'indexed'))
        % NLFILTER(A, 'indexed', [M N], 'fun', P1, ...)
        a = varargin{1};
        nhood = varargin{3};
        fun = varargin{4};
        params = varargin(5:end);
        padval = 1;
        
    else
        % NLFILTER(A, [M N], 'fun', P1, ...)
        a = varargin{1};
        nhood = varargin{2};
        fun = varargin{3};
        params = varargin(4:end);
        padval = 0;
    end
end

if (isa(a,'uint8'))
    padval = 0;
end

% If we have been given an eval-able expression, remake it as an
% inline function object.
if (isstr(fun) & (any(fun<48) | any(fun>=91 & fun<=94)))
    fun = inline(fun,length(params));
end