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annotate inst/mat2gray.m @ 885:40269ff6760d

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imcast: new function to convert image between arbitrary classes. * imcast.m: new function acting as wrapper for im2double, im2single, im2uint8, im2uint16, and im2int16. * imcast.m, imnoise.m, imrotate.m: replace ugly hack using feval with call to imcast. * COPYING: specify license of new function. * INDEX: add new function. * NEWS: add note about new function for release 2.4.0.
author Carnë Draug <carandraug@octave.org>
date Tue, 18 Mar 2014 00:51:13 +0000
parents c45838839d86
children
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1 ## Copyright (C) 1999, 2000 Kai Habel <kai.habel@gmx.de>
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2 ## Copyright (C) 2011, 2012 Carnë Draug <carandraug+dev@gmail.com>
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3 ##
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4 ## This program is free software; you can redistribute it and/or modify it under
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5 ## the terms of the GNU General Public License as published by the Free Software
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6 ## Foundation; either version 3 of the License, or (at your option) any later
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7 ## version.
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8 ##
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9 ## This program is distributed in the hope that it will be useful, but WITHOUT
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10 ## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 ## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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12 ## details.
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13 ##
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14 ## You should have received a copy of the GNU General Public License along with
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15 ## this program; if not, see <http://www.gnu.org/licenses/>.
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16
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17 ## -*- texinfo -*-
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18 ## @deftypefn {Function File} {@var{I} =} mat2gray (@var{M})
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19 ## @deftypefnx {Function File} {@var{I} =} mat2gray (@var{M}, [@var{min} @var{max}])
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20 ## Convert a matrix to an intensity image.
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21 ##
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22 ## The returned matrix @var{I} is a grayscale image, of double class and in the
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23 ## range of values [0, 1]. The optional arguments @var{min} and @var{max} will
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24 ## set the limits of the conversion; values in @var{M} below @var{min} and
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25 ## above @var{max} will be set to 0 and 1 on @var{I} respectively.
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26 ##
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27 ## @var{max} and @var{min} default to the maximum and minimum values of @var{M}.
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28 ##
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29 ## If @var{min} is larger than @var{max}, the `inverse' will be returned. Values
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30 ## in @var{M} above @var{max} will be set to 0 while the ones below @var{min}
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31 ## will be set to 1.
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32 ##
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33 ## @strong{Caution:} For compatibility with @sc{matlab}, if @var{min} and @var{max}
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34 ## are equal (either from being actually being set manually or automatically
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35 ## calculated from the @var{M} min and max values, Octave's mat2gray will truncate
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36 ## all values between [0 1]. For example
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37 ##
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38 ## @example
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39 ## @group
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40 ## mat2gray ([-2 0 0.5 0.9 5], [2 2])
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41 ## @result{} [0 0 0.5 0.9 1]
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42 ## mat2gray ([0.5 0.5 0.5])
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43 ## @result{} [0.5 0.5 0.5]
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44 ## mat2gray ([4 4 4])
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45 ## @result{} [1 1 1]
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46 ## @end group
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47 ## @end example
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48 ##
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49 ## @seealso{gray2ind, ind2gray, rgb2gray, im2double, im2uin16, im2uint8, im2int16}
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50 ## @end deftypefn
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51
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52 function in = mat2gray (in, scale)
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53
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54 if (nargin < 1 || nargin > 2)
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55 print_usage;
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56 elseif (!ismatrix (in) || ischar(in))
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57 error ("mat2gray: first argument must be a matrix");
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58 elseif (nargin == 2 && (!isvector (scale) || numel (scale) != 2))
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59 error ("mat2gray: second argument must be a vector with 2 elements");
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60 endif
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61
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62 if (nargin == 1)
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63 out_min = min (in(:));
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64 out_max = max (in(:));
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65 else
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66 ## see more at the end for the cases where max and min are swapped
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67 out_min = min (scale (1), scale (2));
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68 out_max = max (scale (1), scale (2));
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69 endif
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70
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71 ## since max() and min() return a value of same class as input,
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72 ## need to make this values double or the calculations later may fail
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73 out_min = double (out_min);
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74 out_max = double (out_max);
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75
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76 ## if max and min are the same, matlab seems to simple truncate the input
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77 ## between 0 and 1, and ignores the min/max values set. Don't get the logic
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78 ## but hey! Matlab compatibility
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79 if (out_min == out_max)
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80 in(in>1) = 1;
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81 in(in<0) = 0;
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82 return
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83 endif
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84
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85 ## we are editing the input matrix rather than creating a new one to save
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86 ## memory. We need to make sure it's double though
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87 in = double(in);
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88
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89 ## it's faster to get the index of values between max and min only once
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90 ## than to have it calculated on both sides of the assignment later on. We
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91 ## need to get the index before starting editing
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92 idx = (in > out_min & in < out_max);
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93
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94 in(in <= out_min) = 0;
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95 in(in >= out_max) = 1;
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96 in(idx) = (1/(out_max - out_min)) * (double(in(idx)) - out_min);
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97
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98 ## if the given min and max are in the inverse order...
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99 if (nargin > 1 && scale(1) > scale (2))
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100 ## matlab seems to allow setting the min higher than the max but not by
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101 ## checking which one is actually correct. Seems to just invert it
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102 in = abs (in - 1);
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103 endif
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104
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105 endfunction
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106
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107 %!assert(mat2gray([1 2 3]), [0 0.5 1]); # standard use
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108 %!assert(mat2gray(repmat ([1 2; 3 3], [1 1 3])), repmat ([0 0.5; 1 1], [1 1 3])); # setting min and max
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109 %!assert(mat2gray([1 2 3], [2 2]), [1 1 1]); # equal min and max
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110 %!assert(mat2gray([-1 0 0.5 3], [2 2]), [0 0 0.5 1]); # equal min and max
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111 %!assert(mat2gray(ones(3*0.5)), ones(3*0.5)); # equal min and max from the image (not set)
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112 %!assert(mat2gray([1 2 3], [3 1]), [1 0.5 0]); # max and min inverted