The Triangle Is Not the Colour
A gamut percentage tells you the shape of a panel's colour space. It says nothing about whether the colours land where they should.
The Diagram Everyone Draws Wrong
The CIE 1931 chromaticity diagram — the horseshoe-shaped plot that decorates every display spec sheet — is not a photograph of human colour perception. It is a mathematical projection: a 2D slice of the three-stimulus colour matching data collected by the CIE in 1931, with luminance discarded to leave only hue and saturation. The perceptual spacing is notoriously non-uniform. Equal distances in the green-heavy upper lobe represent far smaller perceptual steps than equal distances in the lower-left (blue) region. A triangle drawn on this diagram looks precise. It is not a reliable map of what your visual system will actually distinguish.
That triangle is a gamut boundary — the set of colours a display can physically produce, traced by connecting the chromaticity coordinates of its three primaries. Inside the triangle: reproducible. Outside: clipped or approximated. The percentage figure — "covers 99 % of DCI-P3" — describes the ratio of the panel's triangle area to the standard's triangle area on that horseshoe plot. It says nothing about where inside those triangles the colours actually fall.
Three Standards, Three Triangles, One Underlying Problem
sRGB, standardised in 1996, was built around the phosphors available in CRT monitors at the time. Its primaries are relatively narrow, its triangle modest. DCI-P3 — the digital cinema standard — has a wider green and red primary, giving it roughly 26 % more area than sRGB on the chromaticity diagram. BT.2020, the UHDTV wide-colour-gamut standard, is larger still: primaries so saturated that no current display technology can physically reach all three corners simultaneously. BT.2020 is a container, not a deliverable.
When a manufacturer says a panel covers a given percentage of one of these triangles, they are comparing geometric areas on that non-uniform horseshoe. A panel that covers 90 % of BT.2020 by area may cover a very different 90 % than its competitor — and the shape and position of the coverage matter far more than the percentage. A panel that is excellent in the green and red corners but rolls off early toward saturated blue delivers a different perceptual result than one with even coverage, even if both report 90 %.
Coverage Is Not Accuracy
Here is the distinction that spec sheets routinely elide: gamut coverage describes what a display can produce; gamut accuracy describes whether it produces the right colours from a given signal.
A wide-gamut panel receiving sRGB-tagged content has a decision to make. If the display or its processing chain does not correctly identify and honour the colour space tag, it maps sRGB values directly onto its wider primaries — effectively stretching every colour outward. Reds become hyper-saturated. Skin tones shift. Grass turns fluorescent. The panel has high coverage; it is also technically wrong on every pixel.
Correct behaviour requires a colour management pipeline: the signal's tagged colour space is recognised, the values are transformed through a transfer matrix (or a full ICC profile) into the display's native space, and the primaries land where the content creator intended. Without that, wide gamut is a liability, not an asset. The delta-E metric only captures this error if you are measuring the right reference at the right target.
HDR complicates things further. HDR10 content is tagged to BT.2020 primaries. A panel covering only 70 % of BT.2020 must gamut-map the out-of-gamut colours — compressing the most saturated values into its actual capability. How that compression is handled is a tone-mapping and gamut-mapping algorithm decision, not a hardware decision, and it varies enormously between implementations. Two panels with identical coverage percentages can produce perceptually opposite results depending on the mapping strategy.
What to Actually Ask
The engineering question is not "what percentage of BT.2020 does this cover?" It is: at each target chromaticity coordinate, how far does the measured output deviate from the target, in ΔE units, under the correct signal conditions? That requires measurement — a spectroradiometer, a pattern generator sending correctly tagged test patches, and software that compares measured primaries and secondaries against the relevant standard's reference values.
Coverage percentage belongs on a marketing slide. Measured ΔE at primary, secondary, and mid-saturation targets — taken after calibration — tells you whether the triangle is being used correctly. A modest gamut hit accurately is more useful than a wide gamut hit approximately. The triangle is a boundary; accuracy is what fills it.