Mercurial > octave
view scripts/image/cubehelix.m @ 31207:1c40fc2344f4 stable
quad2d.m: Add BIST test to cset b0e90ca8e679 (bug #62972)
* quad2d.m: Add BIST test for bug #62972.
author | Rik <rik@octave.org> |
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date | Sun, 28 Aug 2022 14:19:43 -0700 |
parents | 796f54d4ddbf |
children | a40c0b7aa376 |
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######################################################################## ## ## Copyright (C) 2014-2022 The Octave Project Developers ## ## See the file COPYRIGHT.md in the top-level directory of this ## distribution or <https://octave.org/copyright/>. ## ## 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 ## <https://www.gnu.org/licenses/>. ## ######################################################################## ## -*- texinfo -*- ## @deftypefn {} {@var{map} =} cubehelix () ## @deftypefnx {} {@var{map} =} cubehelix (@var{n}) ## @deftypefnx {} {@var{map} =} cubehelix (@var{n}, @var{start}, @var{rots}, @var{hue}, @var{gamma}) ## 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 traversing 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. ## If unspecified, the length of the current colormap, or 64, is used. ## ## Reference: Green, D. A., 2011, ## @cite{A @nospell{colour} scheme for the display of astronomical intensity ## images}, Bulletin of the Astronomical Society of India, 39, 289. ## ## @seealso{colormap} ## @end deftypefn function map = cubehelix (n, start = 0.5, rots = -1.5, hue = 1, gamma = 1) if (nargin > 0) if (! isscalar (n)) error ("cubehelix: N must be a scalar"); endif n = double (n); else hf = get (0, "currentfigure"); if (! isempty (hf)) n = rows (get (hf, "colormap")); else n = 64; endif 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 .^= gamma; amp = hue * fract .* (1-fract) /2; 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 ## A better demo of this colormap would be a 3D plot in NTSC instead of ## RGB values. That would really show what this colormap is about. %!demo %! ## Show the 'cubehelix' colormap profile and as an image %! cmap = cubehelix (256); %! subplot (2, 1, 1); %! rgbplot (cmap, "composite"); %! subplot (2, 1, 2); %! rgbplot (cmap);