The **ciexy2cct** function calculates the Correlated Colour Temperature (CCT) T_{\mathrm{cp}} from given CIE 1931 chromaticity coordinates x and y, also known as normalized tristimumuls values. Any errors in the data set or in results generated with the Lighting Toolbox are not in the liability of the CIE nor me, see licence.

See also: cieuv2cc

Usage:

Tcp = ciexy2cct(x,y,'method')

Where:

Parameter | Description |

`Tcp` | Is a scalar or vector containing the resulting Correlated Colour Temperature(s) (CCT) in K. |

`x and y` | Are the input scalars or vectors containing the CIE 1931 chromaticity coordinates x and y. |

`'method'` | Specifies the determination method:‘Robertson’: (default) Robertson’s calculation algorithm, formerly the only recommended algorithm by the CIE. This method is fast and quite accurate.‘exact’: shortest distance method as described in CIE 15:2018, very accurate but comparably slow. Results may vary with different implementation methods.Both methods return NaN if the colour coordinates lie outside the meaningful interval of \Delta uv < 0.05 from the planckian locus in CIE 1960 chromaticity diagram. |

**Examples**

**Correlated Colour Temperature T_{\mathrm{cp}} for x = 0.3145 and y = 0.2567 using ‘Robertson’ method:**

x = 0.3145; y = 0.2567; Tcp = ciexy2cct(x,y)

Result:

Tcp = 7511

**Correlated Colour Temperature T_{\mathrm{cp}} for x = 0.3145 and y = 0.2567 using ‘exact’ method:**

x = 0.3145; y = 0.2567; Tcp = ciexy2cct(x,y,'exact')

Result:

Tcp = 7516.7

**Correlated Colour Temperature T_{\mathrm{cp}} for several chromaticity coordinates using ‘Robertson’ method:**

x = linspace(0.3,0.4,5) y = linspace(0.3,0.35,5) Tcp = ciexy2cct(x,y,'Robertson')

Result:

x = 0.3000 0.3250 0.3500 0.3750 0.4000 y = 0.3000 0.3125 0.3250 0.3375 0.3500 Tcp = 7738 5906 4671 3825 3246

**References**

`Colorimetry, 4th Edition. Commission International de l’Éclairage (CIE), Vienna Austria, 2018, ISBN: 978-3-902842-13-8 , (DOI: 10.25039/TR.015.2018).`

`Computation of Correlated Color Temperature and Distribution Temperature. In: Journal of the Optical Society of America, vol. 58, no. 11, pp. 1528-1535, 1968, (DOI: 10.1364/JOSA.58.001528).`