/usr/share/octave/packages/image-2.6.1/rgb2lab.m is in octave-image 2.6.1-1.
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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 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 | ## Copyright (C) 2015 Hartmut Gimpel
##
## 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{lab} =} rgb2lab (@var{rgb})
## @deftypefnx {Function File} {@var{lab_map} =} rgb2lab (@var{rgb_map})
## Transform a colormap or image from sRGB to CIE L*a*b* color space.
##
## A color in the RGB space consists of red, green, and blue intensities.
## The input RGB values are interpreted as nonlinear sRGB values
## with the white point D65. This means the input values are assumed to
## be in the colorimetric (sRGB) colorspace.
##
## A color in the CIE L*a*b* (or CIE Lab) space consists of lightness L* and
## two color-opponent dimensions a* and b*. The whitepoint is taken as D65.
## The CIE L*a*b* colorspace is also a colorimetric colorspace. It is designed
## to incorporate the human perception of color differences.
##
## Input values of class double, single, uint8 or uint16 are accepted.
## Output class is generally of type double, only input type single will
## result in an output type of single. The shape of the input is
## conserved.
##
## note: This function returns slightly different values than the Matlab
## version. But it has a better "round trip accuracy" (<2e-5)
## for RGB -> Lab -> RGB.
##
## @seealso{lab2rgb, rgb2xyz, rgb2hsv, rgb2ind, rgb2ntsc}
## @end deftypefn
## Author: Hartmut Gimpel <hg_code@gmx.de>
## algorithm taken from the following book:
## Burger, Burge "Digitale Bildverarbeitung", 3rd edition (2015)
function lab = rgb2lab (rgb)
if (nargin != 1)
print_usage ();
endif
[rgb, cls, sz, is_im, is_nd, is_int] ...
= colorspace_conversion_input_check ("rgb2lab", "RGB", rgb, 0);
## transform from non-linear sRGB values to CIE XYZ values
xyz = rgb2xyz (rgb);
## transform from CIE XYZ values to CIE L*a*b* values
lab = xyz2lab (xyz);
# always return values of type double for Matlab compatibility (exception: type single)
lab = colorspace_conversion_revert (lab, cls, sz, is_im, is_nd, is_int, 1);
endfunction
## Test pure colors, gray and some other colors
## (This set of test values is taken from the book by Burger.)
%!assert (rgb2lab ([0 0 0]), [0, 0, 0], 1e-2)
%!assert (rgb2lab ([1 0 0]), [53.24, 80.09, 67.20], 1e-2)
%!assert (rgb2lab ([1 1 0]), [97.14, -21.55, 94.48], 1e-2)
%!assert (rgb2lab ([0 1 0]), [87.74, -86.18, 83.18], 1e-2)
%!assert (rgb2lab ([0 1 1]), [91.11, -48.09, -14.13], 1e-2)
%!assert (rgb2lab ([0 0 1]), [32.30, 79.19, -107.86], 1e-2)
%!assert (rgb2lab ([1 0 1]), [60.32, 98.24, -60.83], 1e-2)
%!assert (rgb2lab ([1 1 1]), [100, 0.00, 0.00], 1e-2)
%!assert (rgb2lab ([0.5 0.5 0.5]), [53.39, 0.00, 0.00], 1e-2)
%!assert (rgb2lab ([0.75 0 0]), [39.77, 64.51, 54.13], 1e-2)
%!assert (rgb2lab ([0.5 0 0]), [25.42, 47.91, 37.91], 1e-2)
%!assert (rgb2lab ([0.25 0 0]), [9.66, 29.68, 15.24], 1e-2)
%!assert (rgb2lab ([1 0.5 0.5]), [68.11, 48.39, 22.83], 1e-2)
## Test tolarant input checking on floats
%!assert (rgb2lab ([1.5 1 1]), [111.47, 43.42, 17.98], 1e-2)
%!test
%! rgb_map = rand (64, 3);
%! assert (lab2rgb (rgb2lab (rgb_map)), rgb_map, 2e-5);
%!test
%! rgb_img = rand (64, 64, 3);
%! assert (lab2rgb (rgb2lab (rgb_img)), rgb_img, 2e-5);
## support sparse input
%!assert (rgb2lab (sparse ([0 0 1])), sparse ([32.30, 79.19, -107.86]), 1e-2)
%!assert (rgb2lab (sparse ([0 1 1])), sparse ([91.11, -48.09, -14.13]), 1e-2)
%!assert (rgb2lab (sparse ([1 1 1])), sparse ([100, 0.00, 0.00]), 1e-2)
## support integer input (and double output)
%!assert (rgb2lab (uint8([255 255 255])), [100, 0.00, 0.00], 1e-2)
## conserve class of single input
%!assert (class (rgb2lab (single([1 1 1]))), 'single')
## Test input validation
%!error rgb2lab ()
%!error rgb2lab (1,2)
%!error <invalid data type 'cell'> rgb2lab ({1})
%!error <RGB must be a colormap or RGB image> rgb2lab (ones (2,2))
## Test ND input
%!test
%! rgb = rand (16, 16, 3, 5);
%! lab = zeros (size (rgb));
%! for i = 1:5
%! lab(:,:,:,i) = rgb2lab (rgb(:,:,:,i));
%! endfor
%! assert (rgb2lab (rgb), lab)
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