The fractional amounts of the x, y, and z primary colors, specified by the International Committee on Illumination, in a color sample; more precisely, x = X / (X + Y + Z ), y = Y / (X + Y + Z ), z = Z / (X + Y + Z ), where X, Y, and Z are the integrals over wavelength λ of the product of the amount of light emerging from the sample per unit wavelength, and the tristimulus values, x̄(λ), ȳ(λ), and z̄(λ) respectively.