### Copyright (C) 1996 John W. Eaton
###
### 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, 59 Temple Place - Suite 330, Boston, MA
### 02111-1307, USA.

## Convert an octave indexed image to a gray scale intensity image.
##
## Y = ind2gray (X) converts an indexed image to a gray scale intensity
## image.  The current colormap is used to determine the intensities.
## The intensity values lie between 0 and 1 inclusive.
##
## Y = ind2gray (X, map) uses the specified colormap instead of the
## current one in the conversion process.
##
## SEE ALSO: gray2ind, rgb2ntsc, image, colormap

function Y = ind2gray (X, map)

  ## Written by Tony Richardson (amr@mpl.ucsd.edu) July 1994.

  if (nargin < 1 || nargin > 2)
    usage ("ind2gray (X, map)");
  elseif (nargin == 1)
    map = colormap ();
  endif

  ## Convert colormap to intensity values.

  yiq = rgb2ntsc (map);
  y = yiq(:,1);

  ## We need Fortran indexing capability, but be sure to save the user's
  ## preference.

  pref = do_fortran_indexing;

  unwind_protect

    do_fortran_indexing = "true";

    ## Replace indices in the input matrix with indexed values in the output
    ## matrix.

    [rows, cols] = size (X);
    Y = y(X(:));
    Y = reshape (Y, rows, cols);

  unwind_protect_cleanup
    do_fortran_indexing = pref;
  end_unwind_protect

endfunction