Representations of Relative Display Gamut Size

Gamut size of a wide gamut display is usually represented with the ratio of its chromaticity triangle area and the chromaticity triangle area of a standard display in CIE xy color coordinates. Such a chromaticity area ratio (CAR) is a rough relative gamut size, because CIE xy is a nonuniform color coordinate system and display gamut is a volume in color space. The representation of relative gamut size with the ratio of the discernible color numbers in a display gamut and NTSC TV gamut is studied. This ratio is called the discernible color number ratio (DCNR). Discernible color number is counted with CIE94 color difference formula in CIELAB color space. It is found that CAR is larger than DCNR for the display with primary purity higher than NTSC primary purity. For example, the CAR of a practical light-emitting diode (LED) display with respect to NTSC TV is 7.8% overestimated, in which red, green, and blue LED primary wavelengths are 625, 520, and 470 nm, respectively; red, green, and blue LED bandwidths are 20, 40, and 30 nm, respectively. In addition, the DCNRs of wide gamut displays with respect to the object color of the same white illuminant are investigated. It is shown that the gamut size improvement for laser display compared with LED display is not significant.