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annotate scripts/image/colorcube.m @ 17118:c97a26408ee0

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Implement PixelRegion option for imread(). * imread.m: document new option. * private/__imread__.m: parse new option and set defaults. * __magick_read__.cc (calculate region): new option to calculate the region to be read, shifts in memory required, and output image size. (read_indexed_images, read_images): implement reading of only specific regions of an image. (__magick_read__): get octave_scalar_map at start for simplicity.
author Carnë Draug <carandraug@octave.org>
date Wed, 31 Jul 2013 21:28:48 +0100
parents 1a800034d443
children b81b9d079515
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727b74f512af colorcube.m: Add new colormap which maximizes equally spaced colors.
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1 ## Copyright (C) 2012 Rik Wehbring
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {@var{map} =} colorcube ()
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21 ## @deftypefnx {Function File} {@var{map} =} colorcube (@var{n})
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22 ## Create color colormap. This colormap is composed of as many equally
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23 ## spaced colors (not grays) in the RGB color space as possible. If there
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24 ## are not a perfect number @var{n} of regularly spaced colors then the
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25 ## remaining entries in the colormap are gradients of pure red, green, blue,
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26 ## and gray.
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27 ## The argument @var{n} must be a scalar.
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28 ## If unspecified, the length of the current colormap, or 64, is used.
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29 ## @seealso{colormap}
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30 ## @end deftypefn
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31
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32 function map = colorcube (n)
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33
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34 if (nargin == 0)
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35 n = rows (colormap);
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36 elseif (nargin == 1)
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37 if (! isscalar (n))
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1a800034d443 Colormap error() calls now report the input variable which is a problem.
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38 error ("colorcube: N must be a scalar");
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39 endif
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40 else
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41 print_usage ();
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42 endif
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43
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44 if (n < 9)
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45 map = gray (n);
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46 return;
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47 endif
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48
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49 # Create colorcube of evenly spaced points with side length of n^1/3
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50 cubelen = fix (cbrt (n));
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51 reserve = n - cubelen^3;
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52
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53 if (reserve == 0)
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54 # Steal space from blue to put the gray gradient
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55 [r, g, b] = meshgrid (linspace (0,1,cubelen),
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56 linspace (0,1,cubelen),
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57 linspace (0,1,cubelen-1));
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58 else
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59 [r, g, b] = meshgrid (linspace (0,1,cubelen),
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60 linspace (0,1,cubelen),
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61 linspace (0,1,cubelen));
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62 endif
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63
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64 # Create map and weed out grays
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65 map = [r(:), g(:), b(:)];
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66 idx = any (bsxfun (@ne, map(:, 1), map(:, 2:3)), 2);
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67 map = map(idx, :);
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68
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69 # Weed out pure colors
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70 idx = sum (map == 0, 2);
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71 map = map(idx != 2, :);
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72
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73 # Put in remaining gradients of pure red, green, blue, and gray
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74 reserve = n - rows (map) - 1;
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75 csteps = fix (reserve/4);
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76 cstepsz = 1 / csteps;
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77 cgrad = (cstepsz:cstepsz:1)';
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78 gsteps = reserve - 3*csteps;
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79 gstepsz = 1 / gsteps;
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80 ggrad = (gstepsz:gstepsz:1)';
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81 map = [map
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82 cgrad, zeros(csteps, 1), zeros(csteps, 1)
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83 zeros(csteps, 1), cgrad, zeros(csteps, 1)
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84 zeros(csteps, 1), zeros(csteps, 1), cgrad
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85 0, 0, 0
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86 ggrad, ggrad, ggrad];
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87
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88 endfunction
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89
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90
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91 %!demo
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92 %! ## Show the 'colorcube' colormap as an image
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93 %! image (1:64, linspace (0, 1, 64), repmat ((1:64)', 1, 64));
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94 %! axis ([1, 64, 0, 1], "ticy", "xy");
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95 %! colormap (colorcube (64));
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96