Page 70 - Computational Colour Science Using MATLAB

OPTIMIZED COLOUR-DIFFERENCE FORMULAE 57

5.4.3 CIEDE2000

The CIE have recently recommended for trial the CIEDE2000 colour-difference
formula for the evaluation of small colour differences (Luo et al., 2001). Note
that CIELAB DE* is still the current CIE recommendation for the evaluation of
ab
large colour differences (DE* 45).
ab
The CIEDE2000 formula was agreed by a technical committee within Division
1 of the CIE (2001) and includes not only lightness, chroma and hue weighting
functions, but also an interactive term between the chroma and hue differences
for improving the performance for blue colours and a scaling factor for the
CIELAB a* scale for improving the performance for colours close to the
achromatic axis. The new formula is given by Equation (5.16),

2 2 2
0 0 0
DE 00 ¼½ðDL =ðk L S L ÞÞ þðDC =ðk C S C ÞÞ þðDH =ðk H S H ÞÞ
1=2
0 0 ,
þ R T ðDC =ðk C S C ÞÞðDH =ðk H S H Þފ ð5:16Þ
where
2 2 1=2
0 0 ,
S L ¼ 1 þ½0.015ðL 50Þ Š=½20 þðL 50Þ Š
S C ¼ 1 þ 0.045C ,
0
S H ¼ 1 þ 0:015C T.
0
The terms DL , DC and DH are given by
0
0
0
DL ¼ L T L S ,
0
0
0
DC ¼ C T C S ,
0
0
0
0 1=2
0 0 sinðDh =2Þ,
0
DH ¼ 2ðC T C S Þ
where the subscripts S and T refer to the standard and trial, respectively, and
where
Dh ¼ h T h S ,
0
0
0
L ¼ L*,
0
a ¼ð1 þ GÞa*,
0
b ¼ b*,
0
02 02 1=2
0 ,
C ¼ða þ b Þ
and
1
h ¼ tan ðb =a Þ.
0
0
0
The G and T terms are computed using
7 7 7 1=2
G ¼ 0:5 0:5ðC* ab =ðC* ab þ 25 ÞÞ
and