chromatism/src/operations/difference.js

A simple set of utility functions for colours.

import toRadian from '../helpers/to-radian'
import convert from '../helpers/convert-to-type'

export default function difference (colourRefOne, colourRefTwo, l, c) {
  l = l || 1
  c = c || 1

  const Lab1 = convert('cielab', colourRefOne)
  const Lab2 = convert('cielab', colourRefTwo)

  const C1 = Math.sqrt(Math.pow(Lab1.a, 2) + Math.pow(Lab1.b, 2))
  const C2 = Math.sqrt(Math.pow(Lab2.a, 2) + Math.pow(Lab2.b, 2))
  const dC = C1 - C2

  const dL = Lab1.L - Lab2.L
  const da = Lab1.a - Lab2.a
  const db = Lab1.b - Lab2.b

  const dH = Math.sqrt(Math.pow(da, 2) + Math.pow(db, 2) - Math.pow(dC, 2))

  const SL = Lab1.L < 16 ? 0.511 : (0.040975 * Lab1.L) / (1.01765 * Lab1.L)
  const SC = (0.0638 * C1) / (1.0131 * C1)

  const H = Math.atan2(Lab1.b, Lab1.a)
  const H1 = H >= 0 ? H : H + 360

  const T = (H1 >= 164) && (H1 <= 345) ? (0.56 + Math.abs(0.2 * Math.cos(toRadian(H1 + 168)))) : (0.36 + Math.abs(0.4 * Math.cos(toRadian(H1 + 35))))
  const F = Math.pow(C1, 4) / (Math.pow(C1, 4) + 1900)

  const SH = SC * (((F * T) + 1) - F)

  const EqPrt1 = Math.pow((dL / (l * SL)), 2)
  const EqPrt2 = Math.pow((dC / (c * SC)), 2)
  const EqPrt3 = Math.pow((dH / (SH)), 2)

  return Math.sqrt(EqPrt1 + EqPrt2 + EqPrt3)
}