An extension of the iOS class UIColor to provide conversion to and from linear RGB colors.

UIColor+LinearRGB.swift

/// An extension to provide conversion to and from linear RGB colors.
extension UIColor {

    /// A set of non-gamma corrected linear RGB values, in the range [0, 1].
    typealias LinearRGB = (r: CGFloat, g: CGFloat, b: CGFloat)

    /// The inverse companded sRGB components to get non-gamma corrected linear values,
    /// in the range [0, 1].
    var linearRGB: LinearRGB {
        var (r, g, b) = (CGFloat(), CGFloat(), CGFloat())
        getRed(&r, green: &g, blue: &b, alpha: nil)
      
        r = (r > 0.03928) ? pow((r + 0.055) / 1.055, 2.4) : (r / 12.92)
        g = (g > 0.03928) ? pow((g + 0.055) / 1.055, 2.4) : (g / 12.92)
        b = (b > 0.03928) ? pow((b + 0.055) / 1.055, 2.4) : (b / 12.92)
      
        return (r, g, b)
    }

    /// Initializes an sRGB gamma corrected color from linear RGB values.
    /// - parameter rgb: The linear RGB values to be gamma corrected.
    /// - parameter alpha: The alpha value of the color.
    convenience init(linear rgb: LinearRGB, alpha: CGFloat = 1.0) {
        let k: CGFloat = 1.0 / 2.4

        let red = (rgb.r <= 0.00304) ? (12.92 * rgb.r) : (1.055 * pow(rgb.r, k) - 0.055)
        let green = (rgb.g <= 0.00304) ? (12.92 * rgb.g) : (1.055 * pow(rgb.g, k) - 0.055)
        let blue = (rgb.b <= 0.00304) ? (12.92 * rgb.b) : (1.055 * pow(rgb.b, k) - 0.055)

        self.init(red: red, green: green, blue: blue, alpha: alpha)
    }

}