169 lines
6.2 KiB
Matlab
169 lines
6.2 KiB
Matlab
function colors = distinguishable_colors(n_colors,bg,func)
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% DISTINGUISHABLE_COLORS: pick colors that are maximally perceptually distinct
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%
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% When plotting a set of lines, you may want to distinguish them by color.
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% By default, Matlab chooses a small set of colors and cycles among them,
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% and so if you have more than a few lines there will be confusion about
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% which line is which. To fix this problem, one would want to be able to
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% pick a much larger set of distinct colors, where the number of colors
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% equals or exceeds the number of lines you want to plot. Because our
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% ability to distinguish among colors has limits, one should choose these
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% colors to be "maximally perceptually distinguishable."
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%
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% This function generates a set of colors which are distinguishable
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% by reference to the "Lab" color space, which more closely matches
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% human color perception than RGB. Given an initial large list of possible
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% colors, it iteratively chooses the entry in the list that is farthest (in
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% Lab space) from all previously-chosen entries. While this "greedy"
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% algorithm does not yield a global maximum, it is simple and efficient.
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% Moreover, the sequence of colors is consistent no matter how many you
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% request, which facilitates the users' ability to learn the color order
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% and avoids major changes in the appearance of plots when adding or
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% removing lines.
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%
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% Syntax:
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% colors = distinguishable_colors(n_colors)
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% Specify the number of colors you want as a scalar, n_colors. This will
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% generate an n_colors-by-3 matrix, each row representing an RGB
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% color triple. If you don't precisely know how many you will need in
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% advance, there is no harm (other than execution time) in specifying
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% slightly more than you think you will need.
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%
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% colors = distinguishable_colors(n_colors,bg)
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% This syntax allows you to specify the background color, to make sure that
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% your colors are also distinguishable from the background. Default value
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% is white. bg may be specified as an RGB triple or as one of the standard
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% "ColorSpec" strings. You can even specify multiple colors:
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% bg = {'w','k'}
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% or
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% bg = [1 1 1; 0 0 0]
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% will only produce colors that are distinguishable from both white and
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% black.
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%
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% colors = distinguishable_colors(n_colors,bg,rgb2labfunc)
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% By default, distinguishable_colors uses the image processing toolbox's
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% color conversion functions makecform and applycform. Alternatively, you
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% can supply your own color conversion function.
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%
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% Example:
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% c = distinguishable_colors(25);
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% figure
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% image(reshape(c,[1 size(c)]))
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%
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% Example using the file exchange's 'colorspace':
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% func = @(x) colorspace('RGB->Lab',x);
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% c = distinguishable_colors(25,'w',func);
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% Copyright (C) 2005-2010 2010-2011 by Timothy E. Holy
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% Copyright (C) 2017 Dynare Team
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%
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% This file is part of Dynare.
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%
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% Dynare is free software: you can redistribute it and/or modify
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% it under the terms of the GNU General Public License as published by
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% the Free Software Foundation, either version 3 of the License, or
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% (at your option) any later version.
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%
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% Dynare is distributed in the hope that it will be useful,
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% but WITHOUT ANY WARRANTY; without even the implied warranty of
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% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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% GNU General Public License for more details.
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%
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% You should have received a copy of the GNU General Public License
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% along with Dynare. If not, see <http://www.gnu.org/licenses/>.
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% Parse the inputs
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if (nargin < 2)
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bg = [1 1 1]; % default white background
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else
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if iscell(bg)
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% User specified a list of colors as a cell aray
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bgc = bg;
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for i = 1:length(bgc)
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bgc{i} = parsecolor(bgc{i});
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end
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bg = cat(1,bgc{:});
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else
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% User specified a numeric array of colors (n-by-3)
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bg = parsecolor(bg);
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end
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end
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% Generate a sizable number of RGB triples. This represents our space of
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% possible choices. By starting in RGB space, we ensure that all of the
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% colors can be generated by the monitor.
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n_grid = 30; % number of grid divisions along each axis in RGB space
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x = linspace(0,1,n_grid);
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[R,G,B] = ndgrid(x,x,x);
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rgb = [R(:) G(:) B(:)];
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if (n_colors > size(rgb,1)/3)
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error('You can''t readily distinguish that many colors');
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end
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% Convert to Lab color space, which more closely represents human
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% perception
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if (nargin > 2)
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lab = func(rgb);
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bglab = func(bg);
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else
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C = makecform('srgb2lab');
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lab = applycform(rgb,C);
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bglab = applycform(bg,C);
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end
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% If the user specified multiple background colors, compute distances
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% from the candidate colors to the background colors
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mindist2 = inf(size(rgb,1),1);
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for i = 1:size(bglab,1)-1
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dX = bsxfun(@minus,lab,bglab(i,:)); % displacement all colors from bg
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dist2 = sum(dX.^2,2); % square distance
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mindist2 = min(dist2,mindist2); % dist2 to closest previously-chosen color
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end
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% Iteratively pick the color that maximizes the distance to the nearest
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% already-picked color
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colors = zeros(n_colors,3);
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lastlab = bglab(end,:); % initialize by making the "previous" color equal to background
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for i = 1:n_colors
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dX = bsxfun(@minus,lab,lastlab); % displacement of last from all colors on list
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dist2 = sum(dX.^2,2); % square distance
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mindist2 = min(dist2,mindist2); % dist2 to closest previously-chosen color
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[~,index] = max(mindist2); % find the entry farthest from all previously-chosen colors
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colors(i,:) = rgb(index,:); % save for output
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lastlab = lab(index,:); % prepare for next iteration
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end
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end
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function c = parsecolor(s)
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if ischar(s)
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c = colorstr2rgb(s);
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elseif isnumeric(s) && size(s,2) == 3
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c = s;
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else
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error('MATLAB:InvalidColorSpec','Color specification cannot be parsed.');
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end
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end
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function c = colorstr2rgb(c)
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% Convert a color string to an RGB value.
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% This is cribbed from Matlab's whitebg function.
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% Why don't they make this a stand-alone function?
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rgbspec = [1 0 0;0 1 0;0 0 1;1 1 1;0 1 1;1 0 1;1 1 0;0 0 0];
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cspec = 'rgbwcmyk';
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k = find(cspec==c(1));
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if isempty(k)
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error('MATLAB:InvalidColorString','Unknown color string.');
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end
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if k~=3 || length(c)==1
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c = rgbspec(k,:);
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elseif length(c)>2
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if strcmpi(c(1:3),'bla')
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c = [0 0 0];
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elseif strcmpi(c(1:3),'blu')
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c = [0 0 1];
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else
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error('MATLAB:UnknownColorString', 'Unknown color string.');
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end
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end
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end
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