Page 87 - Computational Colour Science Using MATLAB

74 COMPUTING COLOUR DIFFERENCE

% computes colour difference from CIELAB values
% using the CIE94 formula
% lab1 and lab2 must be 3 by 1 or 1 by 3 matrices
% and contain L*, a* and b* values
% The dl, dc and dh components are CIE94 deltas
% see also cielabde, cmcde, and cie00de

dim = size(lab1);
if (dim(1) == 1) | (dim(2) == 1)
lab1 = lab1(:)’; % force to be a row matrix
else
disp(’lab1 must be a row matrix’);
return;
end
if (dim(2) *=3)
disp(’lab1 must be 3 by 1 or 1 by 3’);
return;
end

dim = size(lab2);
if (dim(1) == 1) | (dim(2) == 1)
lab2 = lab2(:)’; % force to be a row matrix
else
disp(’lab2 must be a row matrix’);
return;
end
if (dim(2) *=3)
disp(’lab2 must be 3 by 1 or 1 by 3’);
return;
end

dl = lab2(1)-lab1(1);
dc = sqrt(lab2(2)^2 + lab2(3)^2) - sqrt(lab1(2)^2 + . . .
lab1(3)^2);
dh = sqrt((lab2(2)-lab1(2))^2 + (lab2(3)-lab1(3))^2 - . . .
dc^2);

% get the polarity of the dh term
dh = dh*dhpolarity(lab1,lab2);

% need to compute the weights
Lweight = 1.0;