/usr/share/octave/packages/image-2.6.1/rgb2xyz.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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 | ## 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{xyz} =} rgb2xyz (@var{rgb})
## @deftypefnx {Function File} {@var{xyz_map} =} rgb2xyz (@var{rgb_map})
## Transform a colormap or image from sRGB to CIE XYZ 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 XYZ color space consists of three values X, Y and Z.
## Those values are designed to be colorimetric, meaning that their values
## do not depend on the display device hardware.
##
## 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 -> XYZ -> RGB.
##
## @seealso{xyz2rgb, rgb2lab, 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 xyz = rgb2xyz (rgb)
if (nargin != 1)
print_usage ();
endif
[rgb, cls, sz, is_im, is_nd, is_int] ...
= colorspace_conversion_input_check ("rgb2xyz", "RGB", rgb, 0);
## transform from non-linear sRGB values to linear sRGB values
## (inverse modified gamma transform)
rgb_lin = rgb;
mask = rgb <= 0.04045;
rgb_lin(mask) = rgb(mask) ./ 12.92;
rgb_lin(! mask) = ((rgb(! mask) + 0.055) ./ 1.055) .^2.4;
## transform from linear sRGB values to CIE XYZ with whitepoint D65
## (source of this matrix: book of Burger)
matrix_rgb2xyz_D65 = ...
[0.412453, 0.357580, 0.180423;
0.212671, 0.715160, 0.072169;
0.019334, 0.119193, 0.950227];
# Matlab uses the following slightly different conversion matrix.
# matrix_rgb2xyz_D65 = ...
# [0.4124, 0.3576, 0.1805;
# 0.2126, 0.7152, 0.0722;
# 0.0193, 0.1192, 0.9505];
# open source of this transformation matrix:
# https://de.wikipedia.org/wiki/CIE-Normvalenzsystem#Umrechnung_der_Farbr.C3.A4ume
# on July 30, 2015
xyz = rgb_lin * matrix_rgb2xyz_D65';
# always return values of type double for Matlab compatibility (exception: type single)
xyz = colorspace_conversion_revert (xyz, 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 (rgb2xyz ([0 0 0]), [0, 0, 0], 1e-3)
%!assert (rgb2xyz ([1 0 0]), [0.4125, 0.2127, 0.0193], 1e-3)
%!assert (rgb2xyz ([1 1 0]), [0.7700, 0.9278, 0.1385], 1e-3)
%!assert (rgb2xyz ([0 1 0]), [0.3576, 0.7152, 0.1192], 1e-3)
%!assert (rgb2xyz ([0 1 1]), [0.5380, 0.7873, 1.0694], 1e-3)
%!assert (rgb2xyz ([0 0 1]), [0.1804, 0.0722, 0.9502], 1e-3)
%!assert (rgb2xyz ([1 0 1]), [0.5929, 0.2848, 0.9696], 1e-3)
%!assert (rgb2xyz ([1 1 1]), [0.9505, 1.0000, 1.0888], 1e-3)
%!assert (rgb2xyz ([0.5 0.5 0.5]), [0.2034, 0.2140, 0.2330], 1e-3)
%!assert (rgb2xyz ([0.75 0 0]), [0.2155, 0.1111, 0.0101], 1e-3)
%!assert (rgb2xyz ([0.5 0 0]), [0.0883, 0.0455, 0.0041], 1e-3)
%!assert (rgb2xyz ([0.25 0 0]), [0.0210, 0.0108, 0.0010], 1e-3)
%!assert (rgb2xyz ([1 0.5 0.5]), [0.5276, 0.3812, 0.2482], 1e-3)
## Test tolarant input checking on floats
%!assert (rgb2xyz ([1.5 1 1]), [1.5845, 1.3269, 1.1185], 1e-3)
%!test
%! rgb_map = rand (64, 3);
%! assert (xyz2rgb (rgb2xyz (rgb_map)), rgb_map, 2e-5);
%!test
%! rgb_img = rand (64, 64, 3);
%! assert (xyz2rgb (rgb2xyz (rgb_img)), rgb_img, 2e-5);
## support sparse input
%!assert (rgb2xyz (sparse ([0 0 0])), [0 0 0], 1e-3)
%!assert (rgb2xyz (sparse ([0 0 1])), [0.1804, 0.0722, 0.9502], 1e-3)
## support integer input (and double output)
%!assert (rgb2xyz (uint8([255 255 255])), [0.9505, 1.0000, 1.0888], 1e-3)
## conserve class of single input
%!assert (class (rgb2xyz (single([1 1 1]))), 'single')
## Test input validation
%!error rgb2xyz ()
%!error rgb2xyz (1,2)
%!error <invalid data type 'cell'> rgb2xyz ({1})
%!error <RGB must be a colormap or RGB image> rgb2xyz (ones (2,2))
## Test ND input
%!test
%! rgb = rand (16, 16, 3, 5);
%! xyz = zeros (size (rgb));
%! for i = 1:5
%! xyz(:,:,:,i) = rgb2xyz (rgb(:,:,:,i));
%! endfor
%! assert (rgb2xyz (rgb), xyz)
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