CIE 1976 L*a*b* colour space

CIELAB colour space

three-dimensional, approximately uniform colour space produced by plotting in rectangular coordinates L*, a*, b*, quantities defined by the equations:
L* = 116 f (Y/Y_n) − 16
a* = 500 [f (X/X_n) − f (Y/Y_n)]
b* = 200 [f (Y/Y_n) − f (Z/Z_n)]
where
f (X/X_n) = (X/X_n)^1/3 if (X/X_n) > (6/29)³
f (X/X_n) = (841/108) (X/X_n) + 4/29 if (X/X_n) ≤ (6/29)³
and
f (Y/Y_n) = (Y/Y_n)^1/3 if (Y/Y_n) > (6/29)³
f (Y/Y_n) = (841/108) (Y/Y_n) + 4/29 if (Y/Y_n) ≤ (6/29)³
and
f (Z/Z_n) = (Z/Z_n)^1/3 if (Z/Z_n) > (6/29)³
f (Z/Z_n) = (841/108) (Z/Z_n) + 4/29 if (Z/Z_n) ≤ (6/29)³
and X, Y, Z describe the colour stimulus considered and X_n, Y_n, Z_n describe a specified white achromatic stimulus.

Note 1 to entry: Approximate correlates of lightness, chroma and hue can be calculated as follows:
CIE 1976 lightness
L* = 116 f (Y/Y_n) − 16
where
f (Y/Y_n) = (Y/Y_n)^1/3 if (Y/Y_n) > (6/29)³
f (Y/Y_n) = (841/108) (Y/Y_n) + 4/29 if (Y/Y_n) ≤ (6/29)³
CIE 1976 a, b chroma

CIE 1976 a, b hue angle
h_ab = arctan (b*/a*)

Note 2 to entry: See also CIE 15 Colorimetry.

Note 3 to entry: See also ISO/CIE 11664-4 Colorimetry – Part 4: CIE 1976 L*a*b* Colour Space.

Note 4 to entry: This entry was numbered 845-03-56 in IEC 60050-845:1987.

Note 5 to entry: This entry was numbered 17-157 and 17-173 in CIE S 017:2011.