IEVref: 845-23-076 ID: Language: en Status: Standard Term: CIE 1976 L*a*b* colour space Synonym1: CIELAB colour space [Preferred] Synonym2: Synonym3: Symbol: Definition: three-dimensional, approximately uniform colour space produced by plotting in rectangular coordinates L*, a*, b*, quantities defined by the equations:$\begin{array}{l}L*=116f\left(Y/{Y}_{\text{n}}\right)-16\\ a*=500\left[f\left(X/{X}_{\text{n}}\right)-f\left(Y/{Y}_{\text{n}}\right)\right]\\ b*=200\left[f\left(Y/{Y}_{\text{n}}\right)-f\left(Z/{Z}_{\text{n}}\right)\right]\end{array}$where$f\left(X/{X}_{\text{n}}\right)={\left(X/{X}_{\text{n}}\right)}^{1/3}$ if $\left(X/{X}_{\text{n}}\right)>{\left(6/29\right)}^{3}$ $f\left(X/{X}_{\text{n}}\right)=\left(841/108\right)\left(X/{X}_{\text{n}}\right)+4/29$ if $\left(X/{X}_{\text{n}}\right)\le {\left(6/29\right)}^{3}$ and $f\left(Y/{Y}_{\text{n}}\right)={\left(Y/{Y}_{\text{n}}\right)}^{1/3}$ if $\left(Y/{Y}_{\text{n}}\right)>{\left(6/29\right)}^{3}$ $f\left(Y/{Y}_{\text{n}}\right)=\left(841/108\right)\left(Y/{Y}_{\text{n}}\right)+4/29$ if $\left(Y/{Y}_{\text{n}}\right)\le {\left(6/29\right)}^{3}$ and $f\left(Z/{Z}_{\text{n}}\right)={\left(Z/{Z}_{\text{n}}\right)}^{1/3}$ if $\left(Z/{Z}_{\text{n}}\right)>{\left(6/29\right)}^{3}$ $f\left(Z/{Z}_{\text{n}}\right)=\left(841/108\right)\left(Z/{Z}_{\text{n}}\right)+4/29$ if $\left(Z/{Z}_{\text{n}}\right)\le {\left(6/29\right)}^{3}$ and X, Y, Z describe the colour stimulus considered and Xn, Yn, Zn 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:${L}^{\ast }=116f\left(Y/{Y}_{\text{n}}\right)-16$where$f\left(Y/{Y}_{\text{n}}\right)={\left(Y/{Y}_{\text{n}}\right)}^{1/3}$ if $\left(Y/{Y}_{\text{n}}\right)>{\left(6/29\right)}^{3}$ $f\left(Y/{Y}_{\text{n}}\right)=\left(841/108\right)\left(Y/{Y}_{\text{n}}\right)+4/29$ if $\left(Y/{Y}_{\text{n}}\right)\le {\left(6/29\right)}^{3}$ CIE 1976 a, b chroma: $\Delta {C}_{\text{ab}}^{*}={\left({a}^{*2}+{b}^{*2}\right)}^{1/2}$ CIE 1976 a, b hue angle: ${h}_{\text{ab}}=\mathrm{arctan}\left({b}^{*}/{a}^{*}\right)$ 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. Publication date: 2020-12 Source Replaces: Internal notes: CO remarks: TC/SC remarks: VT remarks: Domain1: Domain2: Domain3: Domain4: Domain5: