chromatism/src/conversions/cieluv.js

A simple set of utility functions for colours.

import getIlluminant from '../helpers/get-illuminant'
import toDegree from '../helpers/to-degree'

export default {
  XYZ: value => {
    const epsilon = 0.008856
    const kappa = 903.3
    const white = getIlluminant('D65')

    const chromeCoordsU = (c) => (c.X * 4) / (c.X + (15 * c.Y) + (3 * c.Z))
    const chromeCoordsV = (c) => (c.Y * 9) / (c.X + (15 * c.Y) + (3 * c.Z))

    const u0 = chromeCoordsU(white)
    const v0 = chromeCoordsV(white)

    const a = (1 / 3) * (((52 * value.L) / (value.u + ((13 * value.L) * u0))) - 1)

    const Y = value.L > (kappa * epsilon) ? (Math.pow(((value.L + 16) / 116), 3)) : value.L / kappa

    const b = -5 * Y
    const d = Y * (((39 * value.L) / (value.v + ((13 * value.L) * v0))) - 5)

    const X = (d - b) / (a - (-1 / 3))
    const Z = (X * a) + b

    return {
      X: X * 100,
      Y: Y * 100,
      Z: Z * 100
    }
  },

  cielch: value => {
    const C = Math.sqrt(Math.pow(value.u, 2) + Math.pow(value.v, 2))
    let h = Math.atan2(value.v, value.u)
    if (h < 0) {
      h += (2 * Math.PI)
    }
    h = toDegree(h)

    return {
      L: value.L,
      C,
      h
    }
  }
}