/usr/share/octave/packages/image-2.2.2/im2uint8.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 80 81 82 83 84 | ## Copyright (C) 2007 Søren Hauberg <soren@hauberg.org>
## Copyright (C) 2012 Carnë Draug <carandraug+dev@gmail.com>
##
## 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{im2} = im2uint8 (@var{im1})
## @deftypefnx {Function File} @var{im2} = im2uint8 (@var{im1}, "indexed")
## Convert input image @var{im1} to uint16 precision.
##
## The following images type are supported: double, single, uint8, uint16, int16,
## binary (logical), indexed. If @var{im1} is an indexed images, the second
## argument must be a string with the value `indexed'.
##
## Processing will depend on the class of the input image @var{im1}:
## @itemize @bullet
## @item uint8 - returns the same as input
## @item uint16, double, single, int16, logical - output will be rescaled for the
## interval of the uint8 class [0 255]
## @item indexed - depends on the input class. No value can be above the max of
## the uint8 class (255).
## @end itemize
##
## @seealso{im2bw, im2double, im2int16, im2single, im2uint16}
## @end deftypefn
function im = im2uint8 (im, indexed = false)
## Input checking (private function that is used for all im2class functions)
im_class = imconversion (nargin, "im2uint8", indexed, im);
if (indexed)
imax = max (im(:));
if (imax > 255)
error ("Too many colors '%d' for an indexed uint8 image", imax);
endif
endif
## for those who may wonder, 255 = intmax ("uint8")
switch im_class
case "uint8"
## do nothing, return the same
case {"single", "double"}
if (indexed)
im = uint8 (im) - 1;
else
im = uint8 (im * 255);
endif
case "logical"
im = uint8 (im) * uint8 (255);
case "uint16"
if (indexed)
im = uint8 (im);
else
## 257 is the ratio between the max of uint8 and uint16
## double (intmax ("uint16")) / double (intmax ("uint8")) == 257
im = uint8 (im / 257);
endif
case "int16"
im = uint8 ((double (im) + double (intmax (im_class)) + 1) / 257);
otherwise
error ("unsupported image class %s", im_class);
endswitch
endfunction
%!assert(im2uint8(uint8([1 2 3])), uint8([1 2 3])); # uint16 returns the same
%!assert(im2uint8(uint16([0 65535])), uint8([0 255])); # basic usage with uint16
%!assert(im2uint8([0 0.5 1]), uint8([0 128 255])); # basic usage with double
%!assert(im2uint8([1 2]), uint8([255 255])); # for double, above 1 is same as 1
%!assert(im2uint8(uint16([3 25]), "indexed"), uint8([3 25])); # test indexed uint8
%!assert(im2uint8([3 25], "indexed"), uint8([2 24])); # test indexed double
%!assert(im2uint8(int16([-32768 0 32768])), uint8([0 128 255])); # test signed integer
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