Mercurial > octave-nkf
view scripts/image/cubehelix.m @ 19645:ed4eeb4314e6
cubehelix: fix for the corner cases when N is 1 or 0.
author | Carnë Draug <carandraug@octave.org> |
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date | Fri, 23 Jan 2015 15:28:45 +0000 |
parents | 5ab6fcf32d1e |
children | e8e3a89fa370 |
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## Copyright (C) 2014 Carnë Draug ## ## This file is part of Octave. ## ## Octave 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. ## ## Octave 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 Octave; see the file COPYING. If not, see ## <http://www.gnu.org/licenses/>. ## -*- texinfo -*- ## @deftypefn {Function File} {@var{map} =} cubehelix () ## @deftypefnx {Function File} {@var{map} =} cubehelix (@var{n}) ## Create cubehelix colormap. ## ## This colormap varies from black to white going though blue, green, and red ## tones while maintaining a monotonically increasing perception of intensity. ## This is achieved by transversing a color cube from black to white through ## a helix, hence the name cubehelix, while taking into account the perceived ## brightness of each channel according to the NTSC specifications from 1953. ## ## @example ## rgbplot (cubehelix (256)) ## @end example ## ## The argument @var{n} must be a scalar and corresponds to the lenght of the ## colormap. Defaults to the length of the current colormap. ## ## Development of this colormap is described in @cite{Green, D. A., 2011, ## "A colour scheme for the display of astronomical intensity images", ## Bulletin of the Astronomical Society of India, 39, 289.}. ## ## @seealso{colormap} ## @end deftypefn ## Author: Carnë Draug <carandraug@octave.org> ## PKG_ADD: colormap ("register", "cubehelix"); ## PKG_DEL: colormap ("unregister", "cubehelix"); function map = cubehelix (n = rows (colormap ()), start = 0.5, rots = -1.5, hue = 1, gamma = 1) if (nargin > 5) print_usage () elseif (! isscalar (n)) error ("cubehelix: N must be a scalar"); endif if (n > 1) coeff = [ -0.14861 -0.29227 1.97294 1.78277 -0.90649 0.00000]; fract = ((0:n-1) / (n-1))'; angle = 2 * pi * (start/3 + 1 + rots*fract); fract = fract .^ gamma; amp = hue * fract .* (1-fract) /2; warning ("off", "Octave:broadcast", "local"); map = fract + amp .* ([cos(angle) sin(angle)] * coeff); ## Clip values (only in case users have changed values of hue or gamma) map(map < 0) = 0; map(map > 1) = 1; elseif (n > 0) map = [0, 0, 0]; else map = zeros (0, 3); endif endfunction %!demo %! subplot (1, 2, 1) %! rgbplot (cubehelix (256), "composite") %! subplot (1, 2, 2) %! rgbplot (cubehelix (256))