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{ RCSid $Id$ } |
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{ |
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Compute Lab color space and color differences from XYZ primaries. |
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|
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5/25/02 G.Ward |
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} |
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Xw = 1; Yw = 1; Zw = 1; { default white } |
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sq(x) : x*x; |
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Ls(Yi) : if(Yi/Yw - .01, 116*(Yi/Yw)^(1/3) - 16, 903.3*Yi/Yw); |
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as(Xi,Yi,Zi) : 500*((Xi/Xw)^(1/3) - (Yi/Yw)^(1/3)); |
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bs(Xi,Yi,Zi) : 200*((Yi/Yw)^(1/3) - (Zi/Zw)^(1/3)); |
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|
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{ CIE 1976 Lab delta E formula } |
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dE76(X1,Y1,Z1,X2,Y2,Z2) : sqrt( sq(Ls(Y1)-Ls(Y2)) |
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+ sq(as(X1,Y1,Z1)-as(X2,Y2,Z2)) |
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+ sq(bs(X1,Y1,Z1)-bs(X2,Y2,Z2)) ); |
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|
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{ CIE 1994 Lab delta E formula } |
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kL = 1; kC = 1; kH = 1; { viewing factors } |
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Cs(Xi,Yi,Zi) : sqrt( sq(as(Xi,Yi,Zi)) + sq(bs(Xi,Yi,Zi)) ); |
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C1s(X1,Y1,Z1,X2,Y2,Z2) : sqrt(Cs(X1,Y1,Z1)*Cs(X2,Y2,Z2)); |
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dHs(X1,Y1,Z1,X2,Y2,Z2) : sqrt( sq(as(X1,Y1,Z1)-as(X2,Y2,Z2)) |
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+ sq(bs(X1,Y1,Z1)-bs(X2,Y2,Z2)) |
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- sq(Cs(X1,Y1,Z1)-Cs(X2,Y2,Z2)) ); |
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dE94(X1,Y1,Z1,X2,Y2,Z2) : sqrt( sq((Ls(X1,Y1,Z1)-Ls(X2,Y2,Z2))/kL) |
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+ sq( (Cs(X1,Y1,Z1)-Cs(X2,Y2,Z2)) / |
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(kC*(1+.048*C1s(X1,Y1,Z1,X2,Y2,Z2))) ) |
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+ sq( dHs(X1,Y1,Z1,X2,Y2,Z2) / |
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(kH*(1+.014*C1s(X1,Y1,Z1,X2,Y2,Z2))) ) ) |
