Page 90 - Computational Colour Science Using MATLAB

IMPLEMENTATIONS AND EXAMPLES 77

[c1,h1] = car2pol([lab1(2) lab1(3)]);
[c2,h2] = car2pol([lab2(2) lab2(3)]);
meanC = (c2+c1)/2;

% compute the G factor using the arithmetic mean chroma
G = 0.5 - 0.5*sqrt((meanC^7)/(meanC^7 + 25^7));

% transform the a* values
lab1(2) = (1 + G)*lab1(2);
lab2(2) = (1 + G)*lab2(2);
% recompute the polar coordinates using the new a*
[c1,h1] = car2pol([lab1(2) lab1(3)]);
[c2,h2] = car2pol([lab2(2) lab2(3)]);

% compute the mean values for use later
meanC = (c2+c1)/2;
meanL = (lab2(1)+lab1(1))/2;
[a1,b1] = pol2car([1,h1]);
[a2,b2] = pol2car([1,h2]);
a = (a1+a2)/2;
b = (b1+b2)/2;
[c,meanH] = car2pol([a b]);

% compute the basic delta values
dh = (h2-h1);
if (dh>180)
dh = dh - 360;
end

dl = lab2(1)-lab1(1);
dc = c2-c1;
dh = 2*sqrt(c1*c2)*sin((dh/2)*pi/180);

T = 1 - 0.17*cos((meanH-30)*pi/180) + 0.24*cos((2*-...
meanH)*pi/180);
T = T + 0.32*cos((3*meanH + 6)*pi/180) - ...
0.20*cos((4*meanH - 63)*pi/180);

dthe = 30*exp(-((meanH-275)/25)^2);
rc = 2*sqrt((meanC^7)/(meanC^7 + 25^7));
rt = -sin(2*dthe*pi/180)*rc;