Page 81 - Computational Colour Science Using MATLAB

68 COMPUTING COLOUR DIFFERENCE

else
disp(’ch must be a row matrix’);
return;
end
if (dim(2) *=2)
disp(’ch must be 2 by 1 or 1 by 2’);
return;
end

C = ch(1);
H = ch(2);

fx = tan(H*pi/180);

a = sqrt(C*C/(1 + fx*fx));

b = a*fx;

if (H < 90.0)
% first quadrant
a = abs(a);
b = abs(b);
elseif (H < 180)
% second quadrant
a = -abs(a);
b = abs(b);
elseif (H < 270)
% third quadrant
a = -abs(a);
b = -abs(b);
else
% fourth quadrant
a = abs(a);
b = -abs(b);
end

5.5.2 Computing colour difference

The function cielabde computes the CIELAB colour difference [Equation (5.10)]
from two L*, a*, b* triplets. This function also returns the component deltas,