/usr/share/octave/packages/image-2.2.2/imdither.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 85 86 87 88 89 90 91 | ## Copyright (C) 2009 Sergey Kirgizov
##
## 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{Y}, @var{newmap}] =} imdither (@var{img})
## @deftypefnx {Function File} {[@var{Y}, @var{newmap}] =} imdither (@var{img}, @
## @var{colors})
## @deftypefnx {Function File} {[@var{Y}, @var{newmap}] =} imdither (@var{img}, @
## @var{colors}, @var{dithtype})
## @deftypefnx {Function File} {[@var{Y}, @var{newmap}] =} imdither (@var{img}, @
## @var{map})
## @deftypefnx {Function File} {[@var{Y}, @var{newmap}] =} imdither (@var{img}, @
## @var{map}, @var{colors})
## @deftypefnx {Function File} {[@var{Y}, @var{newmap}] =} imdither(@var{img}, @
## @var{map}, @var{colors}, @var{dithtype})
## Reduce the number a colors of rgb or indexed image.
##
## Note: this requires the ImageMagick "convert" utility.
## get this from www.imagemagick.org if required
## additional documentation of options is available from the
## convert man page.
##
## where
## @var{dithtype} is a value from list:
##
## @itemize @bullet
## @item "None"
## @item "FloydSteinberg" (default)
## @item "Riemersma"
## @end itemize
##
## @var{colors} is a maximum number of colors in result map
##
## TODO: Add facility to use already created colormap over "-remap" option
##
## BUGS: This function return a 0-based indexed images
## when colormap size is lower or equals to 256 like at cmunique code
## @seealso{cmunique}
##
## @end deftypefn
function [Y, newmap] = imdither (im, p1, p2, p3)
colors="256";
dithtype="FloydSteinberg";
if (nargin < 1)
print_usage;
endif
fname = [tmpnam(),".ppm"];
if (nargin == 1 || isscalar(p1))
# rgb
if (nargin >= 2)
colors=sprintf("%d",p1);
if (nargin >= 3)
dithtype=p2;
endif
endif
opts=["-colors ",colors;"-dither ",dithtype];
imwrite(fname,im(:,:,1),im(:,:,2),im(:,:,3),opts);
[Y,newmap]=cmunique(imread(fname));
delete(fname);
else
if (nargin <= 1)
print_usage;
endif
# indexed
if (nargin >= 3)
colors=sprintf("%d",p2);
if (nargin >= 4)
dithtype=p3;
endif
endif
opts=["-colors ",colors;"-dither ",dithtype];
im (rows(p1)<=256)
imwrite(fname,im,(p1+1),opts);
[Y,newmap]=cmunique(imread(fname));
delete(fname);
endif
endfunction
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