Metameric Failure and Modern Displays

[Myndex]

Just a brief note with some recent references, regarding an emerging accessibility concern for newer, wide gamut display technology.

Red Primary

I've mentioned that sRGB is perhaps the ideal display colorspace for accessible purposes, as the "red" primary color is partially within the visible range for protanopia. Someone with protanopia sees the red primary about 50% darker, but they still may see it somewhat.

This is not true of some of the wider gamut displays, especially Rec2020/2100, aka UHD.

With Display P3, the red primary is expected to be darker than the sRGB red, we have a study planned to examine this with protanopia test subjects.

With UHD/Rec2020, we expect the red primary to be nearly invisible—but this depends on the bandwidth of the primary.

Metameric Failure

Metamerism, as it relates to display technology, is an open research question. It was discovered that using very narrow-band (laser) primaries, which in theory improved gamut size and therefore color fidelity, resulted in the discovery that individual variations in color perception are more prevalent than expected.

Common color primaries in sRGB for instance, are wide-band, and as a result mask many individual variations in color perception.

Individual color perception shifts as we age, and of course CVD has specific color deficits, which can be helped with wider-band primaries, but narrow band primaries exacerbate these color vision anomalies.

Recent References

Metamerism Experts’ Day Debrief - Industry experts gather about the topic of metamerism in London recently. https://imago.org/committees/technical/metamerism-experts-day-debrief/

Mapping Quantitative Observer Metamerism of Displays - a 2023 paper in the Journal of Imaging.
https://www.mdpi.com/2313-433X/9/10/227

Regarding Readability

It is the total luminance signal presented to the visual cortex that is used for reading. For calculating accessible contrast then, we need to consider the relative contribution to total luminance of each primary color of the display. What we find first, is that the red and blue primaries supply little to luminance, and as a generality, saturated red or blue should always be the darkest of two colors.

For the protan, we might go a step farther and discount the red primary contribution by the amount of deficit that a protan (lacking L cones) would experience as it relates to the brightest of two colors tested.

The following flowchart describes this, the values listed in the flowchart apply to sRGB. Other color spaces use different values. We are currently testing this as the next release for the Accessible Readability Criterion.

Thank you for reading

Andrew Somers
Director of Research
Inclusive Reading Technologies, Inc.