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New function for colormap cubehelix. * scripts/image/cubehelix.m: new colormap. This colormap uses all colors while keeping a perceived continuous intensity increase. * NEWS: list new function for 4.2. * doc/interpreter/image.txi: add new function to manual on the colormaps section.
author Carnë Draug <carandraug@octave.org>
date Mon, 29 Dec 2014 18:26:12 +0000
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children ed4eeb4314e6
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5ab6fcf32d1e New function for colormap cubehelix.
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1 ## Copyright (C) 2014 Carnë Draug
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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} =} cubehelix ()
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21 ## @deftypefnx {Function File} {@var{map} =} cubehelix (@var{n})
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22 ## Create cubehelix colormap.
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23 ##
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24 ## This colormap varies from black to white going though blue, green, and red
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25 ## tones while maintaining a monotonically increasing perception of intensity.
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26 ## This is achieved by transversing a color cube from black to white through
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27 ## a helix, hence the name cubehelix, while taking into account the perceived
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28 ## brightness of each channel according to the NTSC specifications from 1953.
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29 ##
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30 ## @example
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31 ## rgbplot (cubehelix (256))
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32 ## @end example
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33 ##
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34 ## The argument @var{n} must be a scalar and corresponds to the lenght of the
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35 ## colormap. Defaults to the length of the current colormap.
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36 ##
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37 ## Development of this colormap is described in @cite{Green, D. A., 2011,
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38 ## "A colour scheme for the display of astronomical intensity images",
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39 ## Bulletin of the Astronomical Society of India, 39, 289.}.
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40 ##
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41 ## @seealso{colormap}
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42 ## @end deftypefn
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43
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44 ## Author: Carnë Draug <carandraug@octave.org>
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45
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46 ## PKG_ADD: colormap ("register", "cubehelix");
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47 ## PKG_DEL: colormap ("unregister", "cubehelix");
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48
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49 function map = cubehelix (n = rows (colormap ()), start = 0.5,
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50 rots = -1.5, hue = 1, gamma = 1)
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51
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52 if (nargin > 5)
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53 print_usage ()
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54 endif
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55
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56 if (! isscalar (n) || n < 1)
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57 error ("cubehelix: N must be a positive scalar");
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58 endif
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59
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60 coeff = [ -0.14861 -0.29227 1.97294
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61 1.78277 -0.90649 0.00000];
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62
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63 fract = ((0:n-1) / (n-1))';
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64 angle = 2 * pi * (start/3 + 1 + rots*fract);
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65 fract = fract .^ gamma;
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66 amp = hue * fract .* (1-fract) /2;
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67 warning ("off", "Octave:broadcast", "local");
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68 map = fract + amp .* ([cos(angle) sin(angle)] * coeff);
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69
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70 ## Clip values (only in case users have changed values of hue or gamma)
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71 map(map < 0) = 0;
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72 map(map > 1) = 1;
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73
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74 endfunction
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75
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76 %!demo
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77 %! subplot (1, 2, 1)
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78 %! rgbplot (cubehelix (256), "composite")
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79 %! subplot (1, 2, 2)
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80 %! rgbplot (cubehelix (256))
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81