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An extension of the iOS class UIColor to provide conversion to and from CIELUV colors.
/// An extension to provide conversion to and from CIELUV colors.
extension UIColor {
/// The CIELUV components of a color - lightness (L) and chromaticity (u,v).
struct CIELUV: Hashable {
/// The lightness component of the color, in the range [0, 100] (darkest to brightest).
var L: CGFloat
/// The green-red chromaticity component of the color, typically in the range [-100, 100].
var u: CGFloat
/// The blue-yellow chromaticity component of the color, typically in the range [-100, 100].
var v: CGFloat
}
/// A set of constant values used to convert to and from CIELUV colors.
private struct Constant {
static let d65 = CIEXYZ(X: 95.047, Y: 100.000, Z: 108.883)
static let ⅓: CGFloat = 1.0 / 3.0
static let ϵ: CGFloat = 216.0 / 24389.0
static let κ: CGFloat = 24389.0 / 27.0
static func fu(_ XYZ: CIEXYZ) -> CGFloat {
return (4.0 * XYZ.X) / (XYZ.X + (15.0 * XYZ.Y) + (3.0 * XYZ.Z))
}
static func fv(_ XYZ: CIEXYZ) -> CGFloat {
return (9.0 * XYZ.Y) / (XYZ.X + (15.0 * XYZ.Y) + (3.0 * XYZ.Z))
}
}
/// The CIELUV components of the color using a d65 illuminant and 2° standard observer.
var Luv: CIELUV {
func fL(_ t: CGFloat) -> CGFloat {
if t <= Constant.ϵ { return t * Constant.κ }
return 116.0 * pow(t, Constant.⅓) - 16.0
}
let XYZ = self.XYZ
let ref = Constant.d65
var L = fL(XYZ.Y / ref.Y)
var u = 13.0 * L * (Constant.fu(XYZ) - Constant.fu(ref))
var v = 13.0 * L * (Constant.fv(XYZ) - Constant.fv(ref))
if L.isNaN { L = 0.0 }
if u.isNaN { u = 0.0 }
if v.isNaN { v = 0.0 }
return CIELUV(L: L, u: u, v: v)
}
/// Initializes a color from CIELUV components.
/// - parameter Luv: The components used to initialize the color.
/// - parameter alpha: The alpha value of the color.
convenience init(_ Luv: CIELUV, alpha: CGFloat = 1.0) {
func fL(_ t: CGFloat) -> CGFloat {
if t <= Constant.κ * Constant.ϵ { return t / Constant.κ }
return pow((t + 16.0) / 116.0, 3.0)
}
let ref = Constant.d65
let u = Luv.u / (13.0 * Luv.L) + Constant.fu(ref)
let v = Luv.v / (13.0 * Luv.L) + Constant.fv(ref)
var Y = fL(Luv.L) * 100.0
var X = (-9.0 * Y * u) / ((u - 4.0) * v - (u * v))
var Z = (9.0 * Y - (15.0 * v * Y) - (v * X)) / (3.0 * v)
if X.isNaN { X = 0.0 }
if Y.isNaN { Y = 0.0 }
if Z.isNaN { Z = 0.0 }
self.init(CIEXYZ(X: X, Y: Y, Z: Z), alpha: alpha)
}
}
@adamgraham
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adamgraham commented May 18, 2019

This requires the CIEXYZ extension declared at https://gist.github.com/adamgraham/677c0c41901f3eafb441951de9bc914c

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