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+## Copyright (C) 1999,2000  Kai Habel
+##
+## 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.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{map_out} =} brighten (@var{map}, @var{beta})
+## @deftypefn {Function File} {@var{map_out} =} brighten (@var{h}, @var{beta})
+## @deftypefnx {Function File} {@var{map_out} =} brighten (@var{beta})
+## Darkens or brightens the given colormap. If the @var{map} argument 
+## is omitted, the function is applied to the current colormap. The first
+## argument can also be a valid graphics handle @var{h}, in which case 
+## @code{brighten} is applied to the colormap associated with this handle.
+##
+## Should the resulting colormap @var{map_out} not be assigned, it will be
+## written to the current colormap.
+##
+## The argument @var{beta} should be a scalar between -1 and 1,
+## where a negative value darkens and a positive value brightens
+## the colormap.
+## @seealso{colormap}
+## @end deftypefn
+
+function Rmap = brighten (m, beta)
+  h = -1;
+  if (nargin == 1)
+    beta = m;
+    m = colormap;
+    h = gcf ();
+  elseif (nargin == 2)
+    if (ishandle (m))
+      h = m;
+      m = get (h, "colormap");
+    elseif ((!is_matrix (m)) || (size (m, 2) != 3))
+      error ("First argument must be a matrix of size nx3 or a handle.");
+    endif
+  else
+    print_usage ();
+  endif
+
+  if ( (!is_scalar (beta)) || (beta <= -1) || (beta >= 1) )
+    error ("brighten(...,beta) beta must be a scalar in the range (-1,1).");
+  endif
+
+  if (beta > 0)
+    gamma = 1 - beta;
+  else
+    gamma = 1 / (1 + beta);
+  endif
+
+  if (nargout == 0)
+    if (ishandle (h))
+      set (h, "colormap", m .^ gamma);
+    else
+      colormap (m .^ gamma);
+    endif
+  else
+    Rmap = m .^ gamma;
+  endif
+
+endfunction