/usr/share/octave/site/m/vlfeat/toolbox/imop/vl_xyz2lab.m is in octave-vlfeat 0.9.17+dfsg0-6build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 | function J=vl_xyz2lab(I,il)
% VL_XYZ2LAB Convert XYZ color space to LAB
% J = VL_XYZ2LAB(I) converts the image from XYZ format to LAB format.
%
% VL_XYZ2LAB(I,IL) uses one of the illuminants A, B, C, E, D50, D55,
% D65, D75, D93. The default illuminatn is E.
%
% See also: VL_XYZ2LUV(), VL_HELP().
% Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
% All rights reserved.
%
% This file is part of the VLFeat library and is made available under
% the terms of the BSD license (see the COPYING file).
if nargin < 2
il='E' ;
end
switch lower(il)
case 'a'
xw = 0.4476 ;
yw = 0.4074 ;
case 'b'
xw = 0.3324 ;
yw = 0.3474 ;
case 'c'
xw = 0.3101 ;
yw = 0.3162 ;
case 'e'
xw = 1/3 ;
yw = 1/3 ;
case 'd50'
xw = 0.3457 ;
yw = 0.3585 ;
case 'd55'
xw = 0.3324 ;
yw = 0.3474 ;
case 'd65'
xw = 0.312713 ;
yw = 0.329016 ;
case 'd75'
xw = 0.299 ;
yw = 0.3149 ;
case 'd93'
xw = 0.2848 ;
yw = 0.2932 ;
end
J=zeros(size(I)) ;
% Reference white
Yw = 1.0 ;
Xw = xw/yw ;
Zw = (1-xw-yw)/yw * Yw ;
% XYZ components
X = I(:,:,1) ;
Y = I(:,:,2) ;
Z = I(:,:,3) ;
x = X/Xw ;
y = Y/Yw ;
z = Z/Zw ;
L = 116 * f(y) - 16 ;
a = 500*(f(x) - f(y)) ;
b = 200*(f(y) - f(z)) ;
J = cat(3,L,a,b) ;
% --------------------------------------------------------------------
function b=f(a)
% --------------------------------------------------------------------
sp = find(a > 0.00856) ;
sm = find(a <= 0.00856) ;
k = 903.3 ;
b=zeros(size(a)) ;
b(sp) = a(sp).^(1/3) ;
b(sm) = (k*a(sm) + 16)/116 ;
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