1## Copyright (C) 1994-2017 John W. Eaton <jwe@octave.org> 2## 3## This program is free software: you can redistribute it and/or modify 4## it under the terms of the GNU General Public License as published by 5## the Free Software Foundation, either version 3 of the License, or 6## (at your option) any later version. 7## 8## This program is distributed in the hope that it will be useful, 9## but WITHOUT ANY WARRANTY; without even the implied warranty of 10## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 11## GNU General Public License for more details. 12## 13## You should have received a copy of the GNU General Public License 14## along with this program. If not, see <http://www.gnu.org/licenses/>. 15 16## -*- texinfo -*- 17## @deftypefn {} {@var{yiq_map} =} rgb2ntsc (@var{rgb_map}) 18## @deftypefnx {} {@var{yiq_img} =} rgb2ntsc (@var{rgb_img}) 19## Transform a colormap or image from red-green-blue (RGB) color space to 20## luminance-chrominance (NTSC) space. The input may be of class uint8, 21## uint16, single, or double. The output is of class double. 22## 23## Implementation Note: 24## The reference matrix for the transformation is 25## 26## @example 27## @group 28## /Y\ 0.299 0.587 0.114 /R\ 29## |I| = 0.596 -0.274 -0.322 |G| 30## \Q/ 0.211 -0.523 0.312 \B/ 31## @end group 32## @end example 33## 34## @noindent 35## as documented in @url{http://en.wikipedia.org/wiki/YIQ} and truncated to 3 36## significant figures. Note: The FCC version of NTSC uses only 2 significant 37## digits and is slightly different. 38## @seealso{ntsc2rgb, rgb2hsv, rgb2ind} 39## @end deftypefn 40 41function yiq = rgb2ntsc (rgb) 42 43 if (nargin != 1) 44 print_usage (); 45 endif 46 47 [rgb, cls, sz, is_im, is_nd, is_int] ... 48 = colorspace_conversion_input_check ("rgb2ntsc", "RGB", rgb, false); 49 50 ## Reference matrix for transformation from http://en.wikipedia.org/wiki/YIQ 51 ## and truncated to 3 significant figures. Matlab uses this matrix for their 52 ## conversion. 53 trans = [ 0.299, 0.596, 0.211; 54 0.587, -0.274, -0.523; 55 0.114, -0.322, 0.312 ]; 56 yiq = rgb * trans; 57 ## Note that if the input is of class single, we also return an image 58 ## of class single. This is Matlab incompatible by design, since 59 ## Matlab always returning class double, is a Matlab bug (see patch #8709) 60 61 yiq = colorspace_conversion_revert (yiq, cls, sz, is_im, is_nd, false); 62 63endfunction 64 65 66## Test pure RED, GREEN, BLUE colors 67%!assert (rgb2ntsc ([1 0 0]), [.299 .596 .211]) 68%!assert (rgb2ntsc ([0 1 0]), [.587 -.274 -.523]) 69%!assert (rgb2ntsc ([0 0 1]), [.114 -.322 .312]) 70 71%!test 72%! rgb_map = rand (64, 3); 73%! assert (ntsc2rgb (rgb2ntsc (rgb_map)), rgb_map, 1e-3); 74 75%!test 76%! rgb_img = rand (64, 64, 3); 77%! assert (ntsc2rgb (rgb2ntsc (rgb_img)), rgb_img, 1e-3); 78 79## test tolerance input checking on floats 80%! assert (rgb2ntsc ([1.5 1 1]), [1.149 0.298 0.105], 1e-3); 81 82## Test input validation 83%!error rgb2ntsc () 84%!error rgb2ntsc (1,2) 85%!error <invalid data type 'cell'> rgb2ntsc ({1}) 86%!error <RGB must be a colormap or RGB image> rgb2ntsc (ones (2,2)) 87 88## Test ND input 89%!test 90%! rgb = rand (16, 16, 3, 5); 91%! yiq = zeros (size (rgb)); 92%! for i = 1:5 93%! yiq(:,:,:,i) = rgb2ntsc (rgb(:,:,:,i)); 94%! endfor 95%! assert (rgb2ntsc (rgb), yiq); 96 97## Test output class and size for input images. 98## Most of the tests only test for colormap input. 99 100%!test 101%! ntsc = rgb2ntsc (rand (10, 10, 3)); 102%! assert (class (ntsc), "double"); 103%! assert (size (ntsc), [10 10 3]); 104 105%!test 106%! ntsc = rgb2ntsc (rand (10, 10, 3, "single")); 107%! assert (class (ntsc), "single"); 108%! assert (size (ntsc), [10 10 3]); 109 110%!test 111%! rgb = (rand (10, 10, 3) * 3 ) - 0.5; # values outside range [0 1] 112%! ntsc = rgb2ntsc (rgb); 113%! assert (class (ntsc), "double"); 114%! assert (size (ntsc), [10 10 3]); 115 116%!test 117%! rgb = (rand (10, 10, 3, "single") * 3 ) - 0.5; # values outside range [0 1] 118%! ntsc = rgb2ntsc (rgb); 119%! assert (class (ntsc), "single"); 120%! assert (size (ntsc), [10 10 3]); 121 122%!test 123%! ntsc = rgb2ntsc (randi ([0 255], 10, 10, 3, "uint8")); 124%! assert (class (ntsc), "double"); 125%! assert (size (ntsc), [10 10 3]); 126 127%!test 128%! ntsc = rgb2ntsc (randi ([0 65535], 10, 10, 3, "uint16")); 129%! assert (class (ntsc), "double"); 130%! assert (size (ntsc), [10 10 3]); 131 132%!test 133%! ntsc = rgb2ntsc (randi ([-128 127], 10, 10, 3, "int8")); 134%! assert (class (ntsc), "double"); 135%! assert (size (ntsc), [10 10 3]); 136 137%!test 138%! rgb_double = reshape ([1 0 0 0 0 1 0 0 0 0 1 0], [2 2 3]); 139%! rgb_uint8 = reshape (uint8 ([255 0 0 0 0 255 0 0 0 0 255 0]), 140%! [2 2 3]); 141%! rgb_int16 = int16 (double (rgb_double * uint16 (65535)) -32768); 142%! expected = reshape ([.299 .587 .114 0 .596 -.274 -.322 0 .211 -.523 .312 0], 143%! [2 2 3]); 144%! 145%! assert (rgb2ntsc (rgb_double), expected); 146%! assert (rgb2ntsc (rgb_uint8), expected); 147%! assert (rgb2ntsc (single (rgb_double)), single (expected)); 148