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colorname.m
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colorname.m
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%COLORNAME Map between color names and RGB values
%
% RGB = COLORNAME(NAME) is the RGB-tristimulus value (1x3) corresponding to
% the color specified by the string NAME. If RGB is a cell-array (1xN) of
% names then RGB is a matrix (Nx3) with each row being the corresponding
% tristimulus.
%
% XYZ = COLORNAME(NAME, 'xyz') as above but the XYZ-tristimulus value
% corresponding to the color specified by the string NAME.
%
% XY = COLORNAME(NAME, 'xy') as above but the xy-chromaticity coordinates
% corresponding to the color specified by the string NAME.
%
% NAME = COLORNAME(RGB) is a string giving the name of the color that is
% closest (Euclidean) to the given RGB-tristimulus value (1x3). If RGB is
% a matrix (Nx3) then return a cell-array (1xN) of color names.
%
% NAME = COLORNAME(XYZ, 'xyz') as above but the color is the closest (Euclidean)
% to the given XYZ-tristimulus value.
%
% NAME = COLORNAME(XYZ, 'xy') as above but the color is the closest (Euclidean)
% to the given xy-chromaticity value with assumed Y=1.
%
% Notes::
% - Color name may contain a wildcard, eg. "?burnt"
% - Based on the standard X11 color database rgb.txt.
% - Tristimulus values are in the range 0 to 1
% Copyright (C) 1993-2017, by Peter I. Corke
%
% This file is part of The Robotics Toolbox for MATLAB (RTB).
%
% RTB is free software: you can redistribute it and/or modify
% it under the terms of the GNU Lesser General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% RTB 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 Lesser General Public License for more details.
%
% You should have received a copy of the GNU Leser General Public License
% along with RTB. If not, see <http://www.gnu.org/licenses/>.
%
% http://www.petercorke.com
function out = colorname(a, varargin)
opt.space = {'rgb', 'xyz', 'xy', 'lab', 'ab'};
opt = tb_optparse(opt, varargin);
persistent rgbtable;
% ensure that the database is loaded
if isempty(rgbtable)
% load mapping table from file
fprintf('loading rgb.txt\n');
f = fopen('data/rgb.txt', 'r');
k = 0;
rgb = [];
names = {};
xy = [];
while ~feof(f)
line = fgets(f);
if line(1) == '#',
continue;
end
[A,count,errm,next] = sscanf(line, '%d %d %d');
if count == 3
k = k + 1;
rgb(k,:) = A' / 255.0;
names{k} = lower( strtrim(line(next:end)) );
end
end
s.rgb = rgb;
s.names = names;
rgbtable = s;
end
if isstr(a)
% map name to rgb/xy
if a(1) == '?'
% just do a wildcard lookup
out = namelookup(rgbtable, a(2:end), opt);
else
out = name2color(rgbtable, a, opt);
end
elseif iscell(a)
% map multiple names to colorspace
out = [];
for name=a
color = name2color(rgbtable, name{1}, opt);
if isempty(color)
warning('Color %s not found', name{1});
end
out = [out; color];
end
else
% map values to strings
out = {};
switch opt.space
case {'rgb', 'xyz', 'lab'}
assert(numcols(a) == 3, 'Color value must have 3 elements');
% convert reference colors to input color space
table = colorspace(['RGB->' opt.space], rgbtable.rgb);
for color=a'
d = distance(color, table');
[~,k] = min(d);
out = [out rgbtable.names{k}];
end
case {'xy', 'ab'}
assert(numcols(a) == 2, 'Color value must have 2 elements');
% convert reference colors to input color space
switch opt.space
case 'xy'
table = colorspace('RGB->XYZ', rgbtable.rgb);
table = table(:,1:2) ./ (sum(table,2)*[1 1]);
case 'ab'
table = colorspace('RGB->Lab', rgbtable.rgb);
table = table(:,2:3);
end
for color=a'
d = distance(color, table');
[~,k] = min(d);
out = [out rgbtable.names{k}];
end
end
if length(out) == 1
out = out{1};
end
end
end
function r = namelookup(table, s, opt)
s = lower(s); % all matching done in lower case
r = {};
count = 1;
for k=1:length(table.names),
if ~isempty( findstr(table.names{k}, s) )
r{count} = table.names{k};
count = count + 1;
end
end
end
function out = name2color(table, s, opt)
s = lower(s); % all matching done in lower case
for k=1:length(table.names),
if strcmp(s, table.names(k)),
rgb = table.rgb(k,:);
switch opt.space
case {'rgb', 'xyz', 'lab'}
out = colorspace(['RGB->' opt.space], rgb);
case 'xy'
XYZ = colorspace('RGB->XYZ', rgb);
out = tristim2cc(XYZ);
case 'ab';
Lab = colorspace('RGB->Lab', rgb);
out = Lab(2:3);
end
return;
end
end
out = [];
end