/usr/share/octave/packages/image-2.4.1/rgb2gray.m is in octave-image 2.4.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 | ## Copyright (C) 2000, 2001 Kai Habel <kai.habel@gmx.de>
## Copyright (C) 2012 Carnë Draug <carandraug+dev@gmail.com>
##
## 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, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} @var{gray}= rgb2gray (@var{rgb})
## Convert RGB image or colormap to grayscale.
##
## If @var{rgb} is an RGB image, the conversion to grayscale is weighted based
## on the luminance values (see @code{rgb2ntsc}). Supported classes are single,
## double, uint8 and uint16.
##
## If @var{rgb} is a colormap it is converted into the YIQ space of ntsc. The
## luminance value (Y) is taken to create a gray colormap.
##
## @seealso{mat2gray, ntsc2rgb, rgb2ind, rgb2ntsc, rgb2ycbcr}
## @end deftypefn
function gray = rgb2gray (rgb)
if (nargin != 1)
print_usage();
endif
if (iscolormap (rgb))
gray = rgb2ntsc (rgb) (:, 1) * ones (1, 3);
elseif (isimage (rgb) && ndims (rgb) == 3)
## multiply each color by the luminance factor (this is also matlab compatible)
## 0.29894 * red + 0.58704 * green + 0.11402 * blue
gray = im2double (rgb) .* permute ([0.29894, 0.58704, 0.11402], [1, 3, 2]);
gray = sum (gray, 3);
switch (class (rgb))
case {"single", "double"}
## do nothing. All is good
case "uint8"
gray = im2uint8 (gray);
case "uint16"
gray = im2uint16 (gray);
otherwise
error ("rgb2gray: unsupported class %s", class(rgb));
endswitch
else
error ("rgb2gray: the input must either be an RGB image or a colormap");
endif
endfunction
# simplest test, double image, each channel on its own and then all maxed
%!shared img
%! img = zeros (2, 2, 3);
%! img(:,:,1) = [1 0; 0 1];
%! img(:,:,2) = [0 1; 0 1];
%! img(:,:,3) = [0 0; 1 1];
%! img = rgb2gray (img);
%!assert ([img(1,1) img(1,2) img(2,1) img(2,2)], [0.29894 0.58704 0.11402 1]);
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