27. CIE Color Specifications Calculated from Reflectance or Transmittance Spectra

Food color is one of the most important determinants of acceptability, and an important specification for most food products. The development of compact and easy-to-use colorimeters and spectrophotometers has made the quantitative measurement of color a routine part of product development and quality assurance. There are several widely employed systems of color specification: Munsell, Commission Internationale de l’Eclairage (CIE) tristimulus, and the more recent CIEL*a*b* system. Available software, often incorporated into modern instruments, enables the investigator to report data in any of the above notations. Understanding the different color specification systems, and the means of interconversion, aids the food scientist in selecting an appropriate means of reporting and comparing color measurements. This laboratory exercise provides example data to calculate the following CIE color specifications from reflectance and transmission spectra: (a) Tristimulus values X, Y, and Z; (b) chromaticity coordinates x and y and luminosity, Y; and (c) dominant wavelength (λ _d) and % purity (using the chromaticity diagram). Using readily available software, interconversion can be done between the CIE Y and chromaticity coordinates and other color specification systems including Munsell and CIEL*a*b*.