1## Copyright (C) 2000, 2001 Kai Habel <kai.habel@gmx.de> 2## Copyright (C) 2012 Carnë Draug <carandraug+dev@gmail.com> 3## 4## This program is free software; you can redistribute it and/or modify it under 5## the terms of the GNU General Public License as published by the Free Software 6## Foundation; either version 3 of the License, or (at your option) any later 7## version. 8## 9## This program is distributed in the hope that it will be useful, but WITHOUT 10## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more 12## details. 13## 14## You should have received a copy of the GNU General Public License along with 15## this program; if not, see <http://www.gnu.org/licenses/>. 16 17## -*- texinfo -*- 18## @deftypefn {Function File} @var{gray}= rgb2gray (@var{rgb}) 19## Convert RGB image or colormap to grayscale. 20## 21## If @var{rgb} is an RGB image, the conversion to grayscale is weighted based 22## on the luminance values (see @code{rgb2ntsc}). Supported classes are single, 23## double, uint8 and uint16. 24## 25## If @var{rgb} is a colormap it is converted into the YIQ space of ntsc. The 26## luminance value (Y) is taken to create a gray colormap. 27## 28## @seealso{mat2gray, ntsc2rgb, rgb2ind, rgb2ntsc, rgb2ycbcr} 29## @end deftypefn 30 31function gray = rgb2gray (rgb) 32 33 if (nargin != 1) 34 print_usage(); 35 endif 36 37 if (iscolormap (rgb)) 38 gray = rgb2ntsc (rgb) (:, 1) * ones (1, 3); 39 40 elseif (isimage (rgb) && ndims (rgb) == 3) 41 cls = class (rgb); 42 if (! isfloat (rgb)) 43 rgb = im2double (rgb); 44 endif 45 46 ## multiply each color by the luminance factor (this is also matlab compatible) 47 ## 0.29894 * red + 0.58704 * green + 0.11402 * blue 48 gray = rgb .* permute ([0.29894, 0.58704, 0.11402], [1, 3, 2]); 49 gray = sum (gray, 3); 50 gray = imcast (gray, cls); 51 else 52 error ("rgb2gray: the input must either be an RGB image or a colormap"); 53 endif 54endfunction 55 56# simplest test, double image, each channel on its own and then all maxed 57%!shared img 58%! img = zeros (2, 2, 3); 59%! img(:,:,1) = [1 0; 0 1]; 60%! img(:,:,2) = [0 1; 0 1]; 61%! img(:,:,3) = [0 0; 1 1]; 62%! img = rgb2gray (img); 63%!assert ([img(1,1) img(1,2) img(2,1) img(2,2)], [0.29894 0.58704 0.11402 1]); 64 65%!assert (class (rgb2gray (single (ones (5, 5, 3)))), "single") 66%!assert (class (rgb2gray (uint8 (ones (5, 5, 3)))), "uint8") 67