Colour Science & Perception
what the eye settles, and what it cannot
Concept

Dominant wavelength — where it appears

The single wavelength whose light, mixed with a chosen white, matches a colour's chromaticity. It is found by drawing a line from the white point through the colour to the spectral locus, and it names a broad or tailed spectrum by the line it acts like; purples have none and take a complementary one.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

A broad green sharpens the blue corner; a broad blue dulls it. For displays with a red at 630 nm, a green at 530 and a blue swept from 440 to 490, each primary a Gaussian spectrum of a stated width, the blue corner's ΔEITP move per unit of margin, white at D65 and 320 cd/m². At the 485 nm blue: ×4.37 with three single wavelengths, ×4.51 with a twenty-nanometre green, ×5.05 with a forty-nanometre green, and ×3.94 with a twenty-nanometre blue.

A broad green sharpens the blue; a broad blue dulls it

ΔEITP makes a display's blue corner sharp or blunt according to its primaries, and the census of single-wavelength primaries found the green deciding how sharp — the 485 nm blue's corner moving 4.37 times a margin against a 530 nm green and 8.19 against a 555 nm one. Real primaries have widths, and the prediction was that a broad green acts as a longer green, raising the spike and moving the turn towards the violet, while a broad blue barely matters. The first half holds: a green forty nanometres wide at 530 nm sharpens the 485 nm corner to 5.05 and moves the turn from 453.7 nm to 451.2, as a single-wavelength green at 535.8 nm would, though its dominant wavelength has moved only to 533. The second half does not: a blue twenty nanometres wide moves the turn by a nanometre but dulls the corner by a tenth, to 3.94. The two widths pull the corner opposite ways, and a display whose green and blue are both broad lands near where its line primaries were. The red, at forty nanometres, still changes nothing that matters.

matching · Gamut A long tail sharpens the blue; a short one barely touches it. With the green's core twenty nanometres wide at 530 nm and a share of its power moved into a tail twenty-five nanometres long, the 485 nm blue corner's move per unit of margin in ΔEITP. A third of the power on the long side takes the corner from ×4.51 to ×5.70, past the symmetric forty-nanometre green's ×5.05; the same share on the short side leaves it at ×4.39.

A green's long tail sharpens the blue; its short tail does not

A quantum-dot green falls steeply on one side and trails on the other, and the prediction was that a tail on its long side, holding a third of its power, would make ΔEITP's blue corner treat the green as a line past 538 nm, further than a symmetric forty-nanometre green's 535.8, because all its spread is on the L side. It does: 540.7 nm, the 485 nm corner rising from ×4.51 to ×5.70. The control is the larger finding. The same tail on the short side costs the green far more purity — 0.77 against the long tail's 0.95 — and moves its equivalent line by under a nanometre and a half. The corner reads the green's ratio of L to M signal, to within a third of a nanometre for every long tail, and not its purity, its centroid or its dominant wavelength; a short tail lowers that ratio less than its colour suggests and brings S signal that pushes the corner back.

matching · Gamut

Named alongside it

The objects these essays reach for when they reach for this one.

ΔEDisplay primariesGamutNarrow band displaysPQ, the perceptual quantiserCone fundamentalsHigh dynamic range

All concepts