How to compute color contrast ratio between two UIColor instances

Question

I\'m looking for a concise way to compute the color contrast ratio between two UIColor instances in Swift. I\'ve found examples that are close but are overly compli

Answer 1

If building for WatchOS where CoreImage is not available or for whatever reason you do not want to rely on CoreImage and therefore CIColor is unavailable, replace @Mobile Dan's luminance function with:

  private func luminance() -> CGFloat {
  // https://www.w3.org/TR/WCAG20-TECHS/G18.html#G18-tests

    func adjust(colorComponent: CGFloat) -> CGFloat {
      return (colorComponent < 0.03928) ? (colorComponent / 12.92) : pow((colorComponent + 0.055) / 1.055, 2.4)
    }

    var red: CGFloat = 0
    var green: CGFloat = 0
    var blue: CGFloat = 0
    var alpha: CGFloat = 0
    getRed(&red, green: &green, blue: &blue, alpha: &alpha)

    return 0.2126 * adjust(colorComponent: red)
      + 0.7152 * adjust(colorComponent: green)
      + 0.0722 * adjust(colorComponent: blue)
  }