Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / image-1.0.15 / houghtf.m

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+## Copyright (C) 2008 Soren Hauberg
+## 
+## This program 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 3 of the License, or
+## (at your option) any later version.
+## 
+## This program 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 this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+## -*- texinfo -*-
+## @deftypefn {Function File} @var{H} = houghtf (@var{bw})
+## @deftypefnx{Function File} @var{H} = houghtf (@var{bw}, @var{method})
+## @deftypefnx{Function File} @var{H} = houghtf (@var{bw}, @var{method}, @var{arg})
+## Perform the Hough transform for lines or circles.
+##
+## The @var{method} argument chooses between the Hough transform for lines and
+## circles. It can be either "line" (default) or "circle".
+##
+## @strong{Line Detection}
+##
+## If @var{method} is "line", the function will compute the Hough transform for
+## lines. A line is parametrised in @var{r} and @var{theta} as
+## @example
+## @var{r} = x*cos(@var{theta}) + y*sin(@var{theta}),
+## @end example
+## where @var{r} is distance between the line and the origin, while @var{theta}
+## is the angle of the vector from the origin to this closest point. The result
+## @var{H} is an @var{N} by @var{M} matrix containing the Hough transform. Here,
+## @var{N} is the number different values of @var{r} that has been attempted.
+## This is computed as @code{2*diag_length - 1}, where @code{diag_length} is
+## the length of the diagonal of the input image. @var{M} is the number of
+## different values of @var{theta}. These can be set through the third input
+## argument @var{arg}. This must be a vector of real numbers, and is by default
+## @code{pi*(-90:90)/180}.
+##
+## @strong{Circle Detection}
+##
+## If @var{method} is "circle" the function will compute the Hough transform for
+## circles. The circles are parametrised in @var{r} which denotes the radius of
+## the circle. The third input argument @var{arg} must be a real vector containing
+## the possible values of @var{r}.
+## If the input image is @var{N} by @var{M}, then the result @var{H} will be an
+## @var{N} by @var{M} by @var{K} array, where @var{K} denotes the number of
+## different values of @var{r}.
+##
+## As an example, the following shows how to compute the Hough transform for circles
+## with radius 3 or 7 in the image @var{im}
+## @example
+## bw = edge(im);
+## H = houghtf(bw, "circle", [3, 7]);
+## @end example
+## Here @var{H} will be an NxMx2 array, where @var{H}(:,:,1) will contain the
+## Hough transform for circles with radius 3, and @var{H}(:,:,2) for radius 7.
+## To find good circles you now need to find local maximas in @var{H}. If you
+## find a local maxima in @var{H}(row, col, 1) it means that a good circle exists
+## with center (row,col) and radius 3. One way to locate maximas is to use the
+## @code{immaximas} function.
+##
+## @seealso{hough_line, hough_circle, immaximas}
+## @end deftypefn
+
+function [accum, R] = houghtf(bw, varargin)
+  ## Default arguments
+  method = "line";
+  args = {};
+  
+  ## Check input arguments
+  if (nargin == 0)
+    error("houghtf: not enough input arguments");
+  endif
+
+  if (!ismatrix(bw) || ndims(bw) != 2)
+    error("houghtf: first arguments must be a 2-dimensional matrix");
+  endif
+
+  if (nargin > 1)
+    if (ischar(varargin{1}))
+      method = varargin{1};
+      args = varargin(2:end);
+    else
+      args = varargin;
+    endif
+  endif
+  
+  ## Choose method
+  switch (lower(method))
+    case "line"
+      [accum, R] = hough_line(bw, args{:});
+    case "circle"
+      accum = hough_circle(bw, args{:});
+    otherwise
+      error("houghtf: unsupported method '%s'", method);
+  endswitch
+
+endfunction