Rec.2020 100% Looking Less Enticing By The Day 

The smallest observer metamerism magnitude (OMM) index was found to be between Rec.709 and DCI-P3, the two display color spaces with the broadest spectra. OMM indices induced by the display Rec.2020 100% are nearly twice as large as those of display Rec.2020 90%.

Effect of color gamut and luminance on observer metamerism in HDR displays, Yongmin Park, Facebook Reality Labs, Michael J. Murdoch, Rochester Institute of Technology (November 2020)

Introduction

“Observer metamerism (OM) refers to the phenomenon that color matches for one observer do not hold for another observer under the same viewing condition. This phenomenon is intrinsically attributed to the fact that human color vision differs from person to person. Various studies pointed out that narrow-band primary displays would increase the possibility of metameric failures, and it can be a severe issue in color critical applications, for example, color grading. As HDR displays are ultimately expected to cover the full extent of Rec.2020 color gamut, it is inevitable for such displays to use extremely spectrally narrow light sources or color filters and/or adding more primaries. Therefore, it is not surprising that OM is regarded as a potential issue of HDR displays. Nonetheless, no extensive studies have been performed to investigate how OM would vary with expansions in the color gamut of displays, because of the lack of ideal HDR displays and difficulty in performing color matching experiments for OM. This paper introduces a simulation-based analysis to look into the effect of color gamut changes on OM in HDR displays. Also, the significance of the effect of peak luminance changes on OM is presented. [S]imulations were performed to understand how OM varies with expansions in chromaticity gamut and increases in peak luminance using the hypothetical displays covering 8 different chromaticity gamuts with peak luminance levels of 500, 1,000, 2,000, and 4,000 cd/m2.”

Effect of Color Gamut

“The simulation results show that OMM goes up steeply with increasing differences in the spectral width between the paired displays. For example, looking at the first row of the matrix in Figure 5, the largest OMM index appears between the display Rec.709 and Rec.2020 100% while the smallest OMM index is witnessed between the display Rec.709 and DCI.P3. As noted in Table 1, the display Rec.2020 100% has the narrowest bandwidth. On the contrary, the display Rec.709 and DCI.P3 are the two displays which have the broadest spectra. It is noteworthy that the OMM indices induced by the display Rec.2020 100% are nearly twice as large as those of display Rec.2020 90% regardless of paired displays except for one case, which is they paired with Rec.2020 95%, respectively.”

Effect of Peak Luminance Level

“The effect of changes in peak luminance on OM was found to be small, increasing OMM by 7 ∼ 8% when peak luminance doubles. In fact, an important finding from the simulation is that the OMM index between a pair of display increases by only a small fraction of the ratio of increase in peak luminance.”

Effect of Reference White Level

“Previous studies pointed out that the reference white level in HDR contents could differ from scene to scene. In this analysis, the mean color differences of individual observers at one reference white level (200 cd/m2) were compared to those at reference white levels: 100, 500, and 1,000 cd/m2. [The results indicate] that reference white level can be regarded as a scalar. Therefore, if the OMM between a display pair is computed with one reference white level, then those between other display pairs for other reference white levels can be predicted using these linear relationships.”

“[D]isplay systems with narrow-band primaries have significantly greater potential for observer metamarism. Thus, despite their potential for other benefits, display manufacturers might want to consider forgoing the use of narrow-band primaries for displays in color-critical applications.”

Mean Observer Metamerism and the Selection of Display Primaries. Mark D. Fairchild and David R. Wyble, Rochester Institute of Technology, Munsell Color Science Laboratory, Rochester, NY/USA

Illustration: Yongmin Park, Michael J. Murdoch