function rgb = labinterp(xi,rgb,xo,varargin)
% Interpolate an sRGB colormap in the Lab colorspace.
%
% Syntax:
%  rgb = labinterp(xi,rgb,xo,<interp1 options>)

M = [...
	+3.2406255,-1.5372080,-0.4986286;...
	-0.9689307,+1.8757561,+0.0415175;...
	+0.0557101,-0.2040211,+1.0569959];
wpt = [0.95047,1,1.08883]; % D65
%
rgb = liRGB2Lab(rgb,M,wpt);
rgb = interp1(xi,rgb,xo,varargin{:});
rgb = liLab2RGB(rgb,M,wpt);
%
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%labinterp
function rgb = liGammaCor(rgb)
% Gamma correction of sRGB data.
idx = rgb <= 0.0031308;
rgb(idx) = 12.92 * rgb(idx);
rgb(~idx) = real(1.055 * rgb(~idx).^(1/2.4) - 0.055);
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%liGammaCor
function rgb = liGammaInv(rgb)
% Inverse gamma correction of sRGB data.
idx = rgb <= 0.04045;
rgb(idx) = rgb(idx) / 12.92;
rgb(~idx) = real(((rgb(~idx) + 0.055) / 1.055).^2.4);
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%liGammaInv
function lab = liRGB2Lab(rgb,M,wpt) % Nx3 <- Nx3
% Convert a matrix of sRGB values to Lab.
%
%lab = applycform(rgb,makecform('srgb2lab','AdaptedWhitePoint',wpt));
%
% RGB2XYZ:
xyz = liGammaInv(rgb) / M.';
% Remember to include my license when copying my implementation.
% XYZ2Lab:
xyz = bsxfun(@rdivide,xyz,wpt);
idx = xyz>(6/29)^3;
F = idx.*(xyz.^(1/3)) + ~idx.*(xyz*(29/6)^2/3+4/29);
lab(:,2:3) = bsxfun(@times,[500,200],F(:,1:2)-F(:,2:3));
lab(:,1) = 116*F(:,2) - 16;
%
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%liRGB2Lab
function rgb = liLab2RGB(lab,M,wpt) % Nx3 <- Nx3
% Convert a matrix of Lab values to sRGB.
%
%rgb = applycform(lab,makecform('lab2srgb','AdaptedWhitePoint',wpt));
%
% Lab2XYZ
tmp = bsxfun(@rdivide,lab(:,[2,1,3]),[500,Inf,-200]);
tmp = bsxfun(@plus,tmp,(lab(:,1)+16)/116);
idx = tmp>(6/29);
tmp = idx.*(tmp.^3) + ~idx.*(3*(6/29)^2*(tmp-4/29));
xyz = bsxfun(@times,tmp,wpt);
% Remember to include my license when copying my implementation.
% XYZ2RGB
rgb = max(0,min(1, liGammaCor(xyz * M.')));
%
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%cbLab2RGB
% Copyright (c) 2017 Stephen Cobeldick
%
% Licensed under the Apache License, Version 2.0 (the "License");
% you may not use this file except in compliance with the License.
% You may obtain a copy of the License at
%
% http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS,
% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
% See the License for the specific language governing permissions and limitations under the License.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%license
