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root/radiance/ray/src/cal/cal/cielab.cal
Revision: 1.1
Committed: Sat Feb 22 02:07:21 2003 UTC (21 years, 2 months ago) by greg
Branch: MAIN
CVS Tags: rad3R5, rad3R6, rad3R6P1
Log Message: 
Changes and check-in for 3.5 release
Includes new source files and modifications not recorded for many years
See ray/doc/notes/ReleaseNotes for notes between 3.1 and 3.5 release

File Contents

# User Rev Content
1 greg 1.1 {
2     Compute Lab color space and color differences from XYZ primaries.
3    
4     5/25/02 G.Ward
5     }
6     Xw = 1; Yw = 1; Zw = 1; { default white }
7     sq(x) : x*x;
8     Ls(Yi) : if(Yi/Yw - .01, 116*(Yi/Yw)^(1/3) - 16, 903.3*Yi/Yw);
9     as(Xi,Yi,Zi) : 500*((Xi/Xw)^(1/3) - (Yi/Yw)^(1/3));
10     bs(Xi,Yi,Zi) : 200*((Yi/Yw)^(1/3) - (Zi/Zw)^(1/3));
11    
12     { CIE 1976 Lab delta E formula }
13     dE76(X1,Y1,Z1,X2,Y2,Z2) : sqrt( sq(Ls(Y1)-Ls(Y2))
14     + sq(as(X1,Y1,Z1)-as(X2,Y2,Z2))
15     + sq(bs(X1,Y1,Z1)-bs(X2,Y2,Z2)) );
16    
17     { CIE 1994 Lab delta E formula }
18     kL = 1; kC = 1; kH = 1; { viewing factors }
19     Cs(Xi,Yi,Zi) : sqrt( sq(as(Xi,Yi,Zi)) + sq(bs(Xi,Yi,Zi)) );
20     C1s(X1,Y1,Z1,X2,Y2,Z2) : sqrt(Cs(X1,Y1,Z1)*Cs(X2,Y2,Z2));
21     dHs(X1,Y1,Z1,X2,Y2,Z2) : sqrt( sq(as(X1,Y1,Z1)-as(X2,Y2,Z2))
22     + sq(bs(X1,Y1,Z1)-bs(X2,Y2,Z2))
23     - sq(Cs(X1,Y1,Z1)-Cs(X2,Y2,Z2)) );
24     dE94(X1,Y1,Z1,X2,Y2,Z2) : sqrt( sq((Ls(X1,Y1,Z1)-Ls(X2,Y2,Z2))/kL)
25     + sq( (Cs(X1,Y1,Z1)-Cs(X2,Y2,Z2)) /
26     (kC*(1+.048*C1s(X1,Y1,Z1,X2,Y2,Z2))) )
27     + sq( dHs(X1,Y1,Z1,X2,Y2,Z2) /
28     (kH*(1+.014*C1s(X1,Y1,Z1,X2,Y2,Z2))) ) )