% -*- texinfo -*-
% @deftypefn {Function File} {@var{filter} = } fspecial(@var{type}, @var{arg1}, @var{arg2})
% Create spatial filters for image processing.
%
% @var{type} determines the shape of the filter and can be
% @table @t
% @item 'average'
% Rectangular averaging filter. The optional argument @var{arg1} controls the
% size of the filter. If @var{arg1} is an integer @var{N}, a @var{N} by @var{N}
% filter is created. If it is a two-vector with elements @var{N} and @var{M}, the
% resulting filter will be @var{N} by @var{M}. By default a 3 by 3 filter is
% created.
% @item 'disk'
% Circular averaging filter. The optional argument @var{arg1} controls the
% radius of the filter. If @var{arg1} is an integer @var{N}, a 2 @var{N} + 1
% filter is created. By default a radius of 5 is used.
% @item 'gaussian'
% Gaussian filter. The optional argument @var{arg1} controls the size of the
% filter. If @var{arg1} is an integer @var{N}, a @var{N} by @var{N}
% filter is created. If it is a two-vector with elements @var{N} and @var{M}, the
% resulting filter will be @var{N} by @var{M}. By default a 3 by 3 filter is
% created. The optional argument @var{arg2} sets spread of the filter. By default
% a spread of @math{0.5} is used.
% @item 'log'
% Laplacian of Gaussian. The optional argument @var{arg1} controls the size of the
% filter. If @var{arg1} is an integer @var{N}, a @var{N} by @var{N}
% filter is created. If it is a two-vector with elements @var{N} and @var{M}, the
% resulting filter will be @var{N} by @var{M}. By default a 5 by 5 filter is
% created. The optional argument @var{arg2} sets spread of the filter. By default
% a spread of @math{0.5} is used.
% @item 'laplacian'
% 3x3 approximation of the laplacian. The filter is approximated as
% @example
% (4/(@var{alpha}+1))*[@var{alpha}/4, (1-@var{alpha})/4, @var{alpha}/4; ...
% (1-@var{alpha})/4, -1, (1-@var{alpha})/4; ...
% @var{alpha}/4, (1-@var{alpha})/4, @var{alpha}/4];
% @end example
% where @var{alpha} is a number between 0 and 1. This number can be controlled
% via the optional input argument @var{arg1}. By default it is @math{0.2}.
% @item 'unsharp'
% Sharpening filter. The following filter is returned
% @example
% (1/(@var{alpha}+1))*[-@var{alpha}, @var{alpha}-1, -@var{alpha}; ...
% @var{alpha}-1, @var{alpha}+5, @var{alpha}-1; ...
% -@var{alpha}, @var{alpha}-1, -@var{alpha}];
% @end example
% where @var{alpha} is a number between 0 and 1. This number can be controlled
% via the optional input argument @var{arg1}. By default it is @math{0.2}.
% @item 'motion'
% Moion blur filter of width 1 pixel. The optional input argument @var{arg1}
% controls the length of the filter, which by default is 9. The argument @var{arg2}
% controls the angle of the filter, which by default is 0 degrees.
% @item 'sobel'
% Horizontal Sobel edge filter. The following filter is returned
% @example
% [ 1, 2, 1;
% 0, 0, 0;
% -1, -2, -1 ]
% @end example
% @item 'prewitt'
% Horizontal Prewitt edge filter. The following filter is returned
% @example
% [ 1, 1, 1;
% 0, 0, 0;
% -1, -1, -1 ]
% @end example
% @item 'kirsch'
% Horizontal Kirsch edge filter. The following filter is returned
% @example
% [ 3, 3, 3;
% 3, 0, 3;
% -5, -5, -5 ]
% @end example
% @end table
% @end deftypefn