## Copyright (C) 2001 Paul Kienzle
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2, or (at your option)
## any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, write to the Free
## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301, USA.

## @deftypefn {Function File} {@var{y} =} filter2 (@var{b, @var{x}})
## @deftypefnx {Function File} {@var{y} =} filter2 (@var{b, @var{x}}, @var{shape})
## Apply the 2-D FIR filter @var{b} to @var{x}. If the argument
## @var{shape} is specified, return an array of the desired shape.
## Possible values are:
##
## @table @asis
## @item 'full'
## pad @var{x} with zeros on all sides before filtering.
## @item 'same'
## unpadded @var{x} (default)
## @item 'valid'
## trim @var{x} after filtering so edge effects are no included.
## @end table
##
## Note this is just a variation on convolution, with the parameters
## reversed and @var{b} rotated 180 degrees.
## @seealso{conv2}
## @end{deftypefn}

## Author: Paul Kienzle <pkienzle@users.sf.net>
## 2001-02-08 
##    * initial release

function Y = filter2 (B, X, shape)

  if (nargin < 2 || nargin > 3)
    usage ("Y = filter2 (B, X [, 'shape'])");
  endif
  if (nargin < 3)
    shape = "same";
  endif

  [nr, nc] = size(B);
  Y = conv2 (X, B(nr:-1:1, nc:-1:1), shape);
endfunction