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author | Torsten Lilge <ttl-octave@mailbox.org> |
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date | Sat, 04 May 2024 17:56:39 +0200 |
parents | 2e484f9f1f18 |
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######################################################################## ## ## Copyright (C) 2018-2024 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} =} rgb2gray (@var{rgb_img}) ## @deftypefnx {} {@var{gray_map} =} rgb2gray (@var{rgb_map}) ## Transform an image or colormap from red-green-blue (RGB) color space to ## a grayscale intensity image. ## ## The input may be of class uint8, int8, uint16, int16, single, or double. ## The output is of the same class as the input. ## ## Implementation Note: ## The grayscale intensity is calculated as ## ## @example ## @group ## @var{I} = 0.298936*@var{R} + 0.587043*@var{G} + 0.114021*@var{B} ## @end group ## @end example ## ## @noindent ## which corresponds to the luminance channel when RGB is translated to ## @nospell{YIQ} as documented in @url{https://en.wikipedia.org/wiki/YIQ}. ## @seealso{rgb2hsv, rgb2ind} ## @end deftypefn function I = rgb2gray (rgb) if (nargin < 1) print_usage (); endif is_int = isinteger (rgb); if (is_int) cls = class (rgb); endif [rgb, sz, is_im, is_nd] ... = colorspace_conversion_input_check ("rgb2gray", "RGB", rgb); ## Reference matrix for transform from http://en.wikipedia.org/wiki/YIQ. ## Matlab uses this matrix for their conversion with oddly more precision. xform = [0.298936; 0.587043; 0.114021]; I = rgb * xform; sz(3) = 1; # grayscale images have 3rd dimension of length 1 I = colorspace_conversion_revert (I, sz, is_im, is_nd); ## Restore integer class if necessary if (is_int) if (cls(end) == "8") # uint8 or int8 I *= 255; if (cls(1) == "i") # int8 I -= 128; endif else # uint16 or int16 I *= 65535; if (cls(1) == "i") # int16 I -= 32768; endif endif I = feval (cls, I); endif endfunction ## Test pure RED, GREEN, BLUE colors %!assert (rgb2gray ([1 0 0]), 0.298936) %!assert (rgb2gray ([0 1 0]), 0.587043) %!assert (rgb2gray ([0 0 1]), 0.114021) ## test tolerance input checking on floats %! assert (rgb2gray ([1.5 1 1]), 1.149468, -1.6e-3); ## Test ND input %!test %! rgb = rand (16, 16, 3, 5); %! I = zeros (16, 16, 1, 5); %! for i = 1:5 %! I(:,:,1,i) = rgb2gray (rgb(:,:,:,i)); %! endfor %! assert (rgb2gray (rgb), I); ## Test output class and size for input images. ## Most of the tests only test for colormap input. %!test %! I = rgb2gray (rand (10, 10, 3)); %! assert (class (I), "double"); %! assert (size (I), [10 10]); %!test %! I = rgb2gray (rand (10, 10, 3, "single")); %! assert (class (I), "single"); %! assert (size (I), [10 10]); %!test %! rgb = (rand (10, 10, 3) * 3 ) - 0.5; # values outside range [0 1] %! I = rgb2gray (rgb); %! assert (class (I), "double"); %! assert (size (I), [10 10]); %!test %! rgb = (rand (10, 10, 3, "single") * 3 ) - 0.5; # values outside range [0 1] %! I = rgb2gray (rgb); %! assert (class (I), "single"); %! assert (size (I), [10 10]); %!test %! I = rgb2gray (randi ([0 255], 10, 10, 3, "uint8")); %! assert (class (I), "uint8"); %! assert (size (I), [10 10]); %!test %! I = rgb2gray (randi ([0 65535], 10, 10, 3, "uint16")); %! assert (class (I), "uint16"); %! assert (size (I), [10 10]); %!test %! I = rgb2gray (randi ([-128 127], 10, 10, 3, "int8")); %! assert (class (I), "int8"); %! assert (size (I), [10 10]); %!test %! I = rgb2gray (randi ([-32768 32767], 10, 10, 3, "int16")); %! assert (class (I), "int16"); %! assert (size (I), [10 10]); %!test %! rgb_double = reshape ([1 0 0 0 0 1 0 0 0 0 1 0], [2 2 3]); %! rgb_uint8 = reshape (uint8 ([255 0 0 0 0 255 0 0 0 0 255 0]), %! [2 2 3]); %! rgb_int16 = int16 (double (rgb_double * uint16 (65535)) - 32768); %! expected = [0.298936, 0.114021; 0.587043, 0.0]; %! %! assert (rgb2gray (rgb_double), expected); %! assert (rgb2gray (rgb_uint8), uint8 (expected*255)); %! assert (rgb2gray (single (rgb_double)), single (expected)); ## Test input validation %!error <Invalid call> rgb2gray () %!error <invalid data type 'cell'> rgb2gray ({1}) %!error <RGB must be a colormap or RGB image> rgb2gray (ones (2,2))