.toXYZ()

Get a color's CIE XYZ values with toXYZ(), the space the other color spaces are defined from. It takes nothing and returns an XYZColor, whose y is the color's relative luminance:

Color(hex: "#00B386").toXYZ()   // XYZColor(x: 0.204, y: 0.340, z: 0.280)

Relative luminance#

y runs from 0 for black to 1 for white, and it's the number WCAG contrast is built on. To check a pair of colors, use contrastRatio(to:method:), which does the math for you.

Converting onward#

XYZ is a step between spaces: from an XYZColor you can go to toRGB(), toLAB() and toLCH(). It has no toColor(), so go through RGB or LCH to draw it, as in xyz.toLCH().toColor().

How it behaves#

The white point is D65. Inside sRGB, x runs from 0 to 0.95, y from 0 to 1 and z from 0 to 1.09; conversions pass through extended sRGB without clipping, so Display P3 colors reach further. A token gives its light-mode value on iOS 17, macOS 14 and later. lerp(_:t:) mixes two XYZColor values in a straight line.

API#

public extension Color {
    func toXYZ() -> XYZColor
}

public struct XYZColor: Hashable, Sendable {
    public let x: CGFloat       // 0 to 0.95 inside sRGB
    public let y: CGFloat       // 0 to 1, relative luminance
    public let z: CGFloat       // 0 to 1.09 inside sRGB
    public let alpha: CGFloat   // 0 to 1

    public init(x: CGFloat, y: CGFloat, z: CGFloat, alpha: CGFloat)

    public func lerp(_ other: XYZColor, t: CGFloat) -> XYZColor
    public func toRGB() -> RGBColor
    public func toLAB() -> LABColor
    public func toLCH() -> LCHColor
}

toXYZ() takes no parameters.

Sources#

• Color+ColorSpaces.swift, which defines toXYZ() on Color.
• The XYZ folder, which defines XYZColor.
• W3C, Web Content Accessibility Guidelines (WCAG) 2.2, which defines relative luminance.

See also

• .contrastRatio(to:method:) Check WCAG 2 and APCA contrast in Swift, and keep your color pairs passing with a unit test.
• .toLAB() Change a color's lightness alone in CIELab, the lightness that decides contrast.
• .toRGB() Read a color's red, green and blue channels, even past sRGB, to hand to other graphics code.
• Glossary of color terms Look up any color term on this site in plain words, from stop and token to chroma and gamut.