Display Gamut Metrology Using Chromaticity Diagram

With the introduction of the International Telecommunication Union-Radiocommunication Sector (ITU-R) Recommendation BT.2020 (Rec. 2020) color space for ultrahigh definition television, the development of wide-gamut displays has become a high priority. To measure the relative gamut sizes of wide-gamut displays, it is herein proposed that the International Commission on Illumination (CIE) 1931 xy chromaticity diagram be used as a practical single metric rather than the nominally perceptually uniform CIE 1976 u'v' chromaticity diagram because of the high correlations between the Rec. 2020 gamut area-coverage ratios in the xy diagram and the volume-coverage ratios in the CIE 1976 L*a*b* and CIE 1976 L*u*v* color spaces. This paper explains why using the perceptually nonuniform xy diagram is counterintuitively appropriate to measure display gamut sizes by presenting a quantitative analysis of the gamut coverage in terms of hue. The argument is made that performing planimetry in the u'v' diagram, whose perceptual uniformity is valid only when the luminance is constant, does not yield accurate display gamut sizes, because the magenta region area is overestimated and the yellow region area is underestimated. Furthermore, some limitations on the use of planimetry for measuring display gamut sizes of multiprimary displays are discussed, and the color light output standard is proposed as a complement to practical planimetry using the xy diagram.