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########################################################################
##
## Copyright (C) 1994-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## 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 3 of the License, 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, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{I} =} ind2gray (@var{x}, @var{map})
## Convert a color indexed image to a grayscale intensity image.
##
## The image @var{x} must be an indexed image which will be converted using the
## colormap @var{map}. If @var{map} does not contain enough colors for the
## image, pixels in @var{x} outside the range are mapped to the last color in
## the map before conversion to grayscale.
##
## The output @var{I} is of the same class as the input @var{x} and may be
## one of @code{uint8}, @code{uint16}, @code{single}, or @code{double}.
##
## Implementation Note: There are several ways of converting colors to
## grayscale intensities. This functions uses the luminance value obtained
## from @code{rgb2gray} which is @code{I = 0.299*R + 0.587*G + 0.114*B}.
## Other possibilities include the value component from @code{rgb2hsv} or
## using a single color channel from @code{ind2rgb}.
## @seealso{gray2ind, ind2rgb}
## @end deftypefn
function I = ind2gray (x, map)
if (nargin != 2)
print_usage ();
endif
[x, map] = ind2x ("ind2gray", x, map);
## Convert colormap to luminance intensity values
map *= [0.29894; 0.58704; 0.11402];
## Convert colormap to same class as that of input so that reshape
## will produce output of the same type as the input.
cls = class (x);
if (isinteger (x))
## if we later add support for int16 images, this will not work. Look into
## im2int16 from image package for such case
map *= intmax (cls);
elseif (strcmp (cls, "single"))
map = single (map);
endif
## Replace indices in the input matrix with the indexed luminance value.
I = reshape (map(x(:)), size (x));
endfunction
%!shared i2g
%! i2g = ind2gray (1:100, gray (100));
%!
%!assert (i2g, 0:1/99:1, eps)
%!assert (gray2ind (i2g, 100), uint8 (0:99))
## Test input validation
%!error <Invalid call> ind2gray ()
%!error <Invalid call> ind2gray (1)
%!error <X must be an indexed image> ind2gray (ones (3,3,3), jet (64))
%!error <X must be an indexed image> ind2gray (1+i, jet (64))
%!error <X must be an indexed image> ind2gray (sparse (1), jet (64))
%!error <X must be an indexed image> ind2gray (1.1, jet (64))
%!error <X must be an indexed image> ind2gray ({1}, jet (64))
%!error <MAP must be a valid colormap> ind2gray (1, {1})
%!error <MAP must be a valid colormap> ind2gray (1, 1+i)
%!error <MAP must be a valid colormap> ind2gray (1, ones (2,2,2))
%!error <MAP must be a valid colormap> ind2gray (1, ones (2,4))
%!error <MAP must be a valid colormap> ind2gray (1, [-1])
%!error <MAP must be a valid colormap> ind2gray (1, [2])
%!warning <contains colors outside of colormap> ind2gray ([0 1 2], gray (5));
%!warning <contains colors outside of colormap> ind2gray ([1 2 6], gray (5));
%!warning <contains colors outside of colormap> ind2gray (uint8 ([1 2 5]), gray (5));
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