% -*- texinfo -*-
% @deftypefn {Function File} @var{result} = deriche(@var{img}, @var{alpha}, @var{method})
% Deriche 2D image gradient using recursive filters. Precessing time is
% independent of alpha.
% taken from:
% Klette, Zamperoni: Handbuch der Operatoren f� die Bildverarbeitung, vieweg
% 2.Aufl. 1995 pp 224-229
% algorithm: Deriche R.: Fast algorithms for low-level vision: IEEE Trans.
% PAMI-12 (1990) pp 78-87
%
% @table @code
% @item @var{img}
% Input image (as matrix of doubles).
% @item @var{alpha}
% Filter paramter (scale).
% @item method
% If 0 (default) magnitude of gradient, and if 1
% vector gradient (last index 1 for H, 2 for V)
% @end table
%
% Due to the inherent recursive nature of the algorithms the octave
% implementation is rather slow compared to a C implementation although I have
% vectorized it as far as possible at the expense of memory consuption. As a
% side effect the evaluation order had to be modified compared to the Klette /
% Zamperoni approach. (A C Implementation can easily process PAL a video stream in
% realtime on moderate hardware.)
% @end deftypefn