/usr/share/octave/packages/image-2.2.2/intlut.m is in octave-image 2.2.2-1.
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 | ## Copyright (C) 2013 Carnë Draug <carandraug@octave.org>
##
## 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} {} intlut (@var{A}, @var{LUT})
## Convert matrix from look up table (LUT).
##
## Replaces the values from the matrix @var{A} with the corresponding value
## from the look up table @var{LUT} (this is the grayscale equivalent to an
## indexed image).
##
## @var{A} and @var{LUT} must be of the same class, and uint8, uint16, or int16.
## @var{LUT} must have exactly 256 elements for class uint8, and 65536 for
## classes uint16 and int16. Output is of same class as @var{LUT}.
##
## @seealso{ind2gray, ind2rgb, rgb2ind}
## @end deftypefn
function B = intlut (A, LUT)
if (nargin != 2)
print_usage ();
elseif (! strcmp (class (A), class (LUT)))
error ("intlut: A and LUT must be of same class");
elseif (! isvector (LUT))
error ("intlut: LUT must be a vector");
endif
cl= class (A);
switch (cl)
case {"uint8"}, max_numel = 256;
case {"int16", "uint16"}, max_numel = 65536;
otherwise
error ("intlut: A must be of class uint8, uint16, or int16");
endswitch
if (max_numel != numel (LUT))
error ("intlut: LUT must have %d elements for class %s", max_numel, cl);
endif
## We need to convert to double in case of the values in A is
## equal to intmax (class (A))
A = double (A);
if (strcmp ("int16", cl))
A += 32769;
else
A += 1;
endif
B = LUT(A);
endfunction
%!demo
%! ## Returns an uint8 array [254 253 252 251]
%! intlut (uint8 ([1 2 3 4]), uint8 ([255:-1:0]));
%!assert (intlut (uint8 (1:4), uint8 ( 255:-1:0)), uint8 (254:-1:251));
%!assert (intlut (uint16 (1:4), uint16 (65535:-1:0)), uint16 (65534:-1:65531));
%!assert (intlut (int16 (1:4), int16 (32767:-1:-32768)), int16 (-2:-1:-5));
%!assert (intlut (uint8 (255), uint8 (0:255)), uint8 (255));
%!assert (intlut (uint16 (65535), uint16 (0:65535)), uint16 (65535));
%!assert (intlut (int16 (32767), int16 (-32768:32767)), int16 (32767));
%!error intlut ()
%!error intlut ("text")
%!error <class> intlut (1:20, uint8(0:255));
%!error <class> intlut (uint16(1:20), uint8(0:255));
%!error <have 256 elements> intlut (uint8 (1:20), uint8 (0:200));
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