/usr/share/octave/packages/image-2.2.2/stretchlim.m is in octave-image 2.2.2-1.
This file is owned by root:root, with mode 0o644.
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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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 | ## Copyright (C) 2004 Josep Mones i Teixidor <jmones@puntbarra.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{LOW_HIGH} = } stretchlim (@var{I},@var{TOL})
## @deftypefnx {Function File} {@var{LOW_HIGH} = } stretchlim (@var{I})
## @deftypefnx {Function File} {@var{LOW_HIGH} = } stretchlim (@var{RGB},@var{TOL})
## @deftypefnx {Function File} {@var{LOW_HIGH} = } stretchlim (@var{RGB})
## Finds limits to contrast stretch an image
##
## @code{LOW_HIGH=stretchlim(I,TOL)} returns a vector @var{LOW_HIGH}
## which contains a pair of intensities which can be used in
## @code{imadjust} to stretch the contrast of an image, first of them
## will be lower value (@code{imadjust} would assign 0 to it) and second
## is the upper bound. @var{TOL} specifies the fraction of the image to
## saturate at lower and upper limits. It can be a vector of length 2:
## @code{[LOW_FRACT, HIGH_FRACT]}, or it can be a scalar, in that case
## @code{[LOW_FRACT, HIGH_FRACT]=[TOL, 1-TOL]}.
##
## @var{TOL} can't be larger than 0.50 and for TOL=0 then
## @code{LOW_HIGH=[min(I(:)), max(I(:))]}.
##
## @code{LOW_HIGH=stretchlim(I)} behaves as described but defaults
## @var{TOL} to @code{[0.01, 0.99]}.
##
## @code{LOW_HIGH=stretchlim(RGB,TOL)} returns a 2-by-3 matrix in
## @var{LOW_HIGH} of lower and upper values to saturate for each plane
## of the RGB image in M-by-N-by-3 array @var{RGB}. @var{TOL} is a
## vector or a scalar, as described above, and the same fractions are
## applied for each plane.
##
## @code{LOW_HIGH=stretchlim(RGB)} uses @code{[0.01, 0.99]} as default
## value for @var{TOL}.
##
## @strong{Notes:}
##
## Values in @var{LOW_HIGH} are of type double and comprised between 0
## and 1 regardless class of input image.
##
## @strong{Compatibility notes:}
##
## @itemize @bullet
## @item
## int* and uint* types are still not implemented (waiting for support
## in Octave 2.1.58).
## @item
## This function tries to find limits that are nearer to saturate
## requested interval. So, for instance, if you requested a 5% and it
## has to choose between discarding a 1% and a 7%, it will choose the
## later despite being more than requested. This should be test against
## MATLAB behaviour.
## @end itemize
##
## @seealso{imadjust}
## @end deftypefn
function LOW_HIGH = stretchlim(image, TOL)
if (nargin<1 || nargin>2)
print_usage;
endif
if(!ismatrix(image) || ischar(image))
error("stretchlim: image should be a matrix");
endif
## Prepare limits
if(nargin==1)
low_count=0.01;
high_count=0.01; ## we use this definition in __stretchlim_plane__
else
if(isscalar(TOL))
if(TOL<0 || TOL>=0.5)
error("stretchlim: TOL out of bounds. Expected: 0<=TOL<0.5");
endif
low_count=TOL;
high_count=TOL; ## as before...
elseif(isvector(TOL))
if(length(TOL)!=2)
error("stretchlim: TOL length must be 2.");
endif
low_count=TOL(1);
high_count=1-TOL(2); ## as before...
else
error("stretchlim: TOL contains an invalid value.");
endif
endif
## well use size of image several times...
simage=size(image);
## Convert fractions to pixels
psimage=prod(simage(1:2));
low_count*=psimage;
high_count*=psimage;
if(length(simage)<=2)
## intensity
LOW_HIGH=__stretchlim_plane__(image, low_count, high_count);
elseif(length(simage)==3 && simage(3)==3)
## RGB
LOW_HIGH=zeros(2,3);
for i=1:3
LOW_HIGH(:,i)=__stretchlim_plane__(image(:,:,i), low_count, ...
high_count);
endfor
else
error("stretchlim: invalid image.");
endif
endfunction
## Processes a plane
## high_count is defined so that high_count=elements is the same as
## low_count=elements (and not total_elements-elements)
function LOW_HIGH = __stretchlim_plane__(plane, low_count, high_count)
## check exceptions
if(low_count==0 && high_count==0)
LOW_HIGH=[min(plane(:)); max(plane(:))];
else
## we sort values
sorted=sort(plane(:));
low=sorted(round(low_count+1));
pos=find(sorted>low);
if(length(pos)>0)
low2=sorted(pos(1));
d1=low_count-sum(sorted<low);
d2=sum(sorted<low2)-low_count;
if(d2<d1)
low=low2;
endif
endif
high=sorted(end-round(high_count));
pos=find(sorted<high);
if(length(pos)>0)
high2=sorted(pos(end));
d1=high_count-sum(sorted>high);
d2=sum(sorted>high2)-high_count;
if(d2<d1)
high=high2;
endif
endif
## set result variable
LOW_HIGH=[low;high];
endif
endfunction
%!demo
%! stretchlim([1:100])
%! # This discards 1% of data from each end, 1 and 100.
%! # So result should be [2;99]
%!# some invalid params
%!error(stretchlim());
%!error(stretchlim("bad parameter"));
%!error(stretchlim(zeros(10,10,4)));
%!error(stretchlim(zeros(10,10,3,2)));
%!error(stretchlim(zeros(10,10),"bad parameter"));
%!error(stretchlim(zeros(10,10),0.01,2));
%!# default param
%!assert(stretchlim([1:100]),[2;99]);
%!# scalar TOL
%!assert(stretchlim([1:100],0.01),[2;99]);
%!# vector TOL
%!assert(stretchlim([1:100],[0.01,0.98]),[2;98]);
%!# TOL=0
%!assert(stretchlim([1:100],0),[1;100]);
%!# non uniform histogram tests
%!assert(stretchlim([1,ones(1,90)*2,92:100],0.05),[2;95]);
%!assert(stretchlim([1,ones(1,4)*2,6:100],0.05),[6;95]);
%!# test limit rounding...
%!assert(stretchlim([1,ones(1,5)*2,7:100],0.05),[7;95]); # 6% lost
%!assert(stretchlim([1,ones(1,6)*2,8:100],0.05),[8;95]); # 7% lost
%!assert(stretchlim([1,ones(1,7)*2,9:100],0.05),[9;95]); # 8% lost
%!assert(stretchlim([1,ones(1,8)*2,10:100],0.05),[2;95]); # now he limit at 2 => 1% lost
%!# test RGB
%!test
%! RGB=zeros(100,1,3);
%! RGB(:,:,1)=[1:100];
%! RGB(:,:,2)=[2:2:200];
%! RGB(:,:,3)=[4:4:400];
%! assert(stretchlim(RGB),[2,4,8;99,198,396]);
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