colors-LUV.lua

XYZA.EPSILON = math.pow(6 / 29, 3)
XYZA.KAPPA = math.pow(29 / 3, 3)
XYZA.WHITE = XYZA.fromRGBA(255,255,255,1)

function bit2linear(channel)
  --[[
  http://www.brucelindbloom.com/Eqn_RGB_to_XYZ.html
	This converts rgb 8bit to rgb linear, lazy because the other algorithm is really really dumb
  ]]
	-- return Math.pow(channel, 2.2); -- use in shader cores

	-- CSS Colors Level 4 says 0.03928, Bruce Lindbloom who cared to write all algos says 0.04045, used bruce because whynawt
  if channel <= 0.04045 then
    return channel / 12.92
  else
    return math.pow((channel + 0.055) / 1.055, 2.4)
  end
end

local LUVA = {}

LUVA.deltaGammaFactor = 1 / (XYZA.WHITE.x + 15 * XYZA.WHITE.y + 3 * XYZA.WHITE.z)
LUVA.uDeltaGamma = 4 * XYZA.WHITE.x * LUVA.deltaGammaFactor
LUVA.vDeltaGamma = 4 * XYZA.WHITE.y * LUVA.deltaGammaFactor

function LUVA.new(L,u,v,a)
  n = {l=l, u=u, v=v, a=a}
  setmetatable(n, LUVA)
  return n
end

function LUVA.fromRGBA(r,g,b,a)
	-- XYZA first
	local R = bit2linear(r)
	local G = bit2linear(g)
	local B = bit2linear(b)
	local X = 0.412453 * R + 0.357580 * G + 0.180423 * B
	local Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
	local Z = 0.019334 * R + 0.119193 * G + 0.950227 * B

	local yGamma = Y / XYZA.WHITE.y
	local deltaDivider = X + 15 * Y + 3 * Z
	if deltaDivider == 0 then deltaDivider = 1 end
	local deltaFactor = 1 / deltaDivider

	local uDelta = 4 * X * deltaFactor
	local vDelta = 9 * Y * deltaFactor
	local L
	if yGamma > XYZA.EPSILON then
		L = 116 * math.pow(yGamma, 1./3) - 16
	else
		L = XYZA.KAPPA * yGamma
	end
	local u = 13 * L * (uDelta - LUVA.uDeltaGamma)
	local v = 13 * L * (vDelta - LUVA.vDeltaGamma)
	return LUVA.new(L, u, v, a)
end

return LUVA

code ripped from SirStendec here https://github.com/FrankerFaceZ/FrankerFaceZ/blob/master/src/utilities/color.js#L59