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## -*- texinfo -*-
## @deftypefn  {} {@var{y} =} filter2 (@var{b}, @var{x})
## @deftypefnx {} {@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 @qcode{"full"}
## pad @var{x} with zeros on all sides before filtering.
##
## @item @qcode{"same"}
## unpadded @var{x} (default)
##
## @item @qcode{"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

function y = filter2 (b, x, shape)

  if (nargin < 2)
    print_usage ();
  endif
  if (nargin < 3)
    shape = "same";
  endif

  [nr, nc] = size (b);
  y = conv2 (x, b(nr:-1:1, nc:-1:1), shape);

endfunction