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

Colour order systems — where it appears

Arrangements of physical samples on a regular lattice so that a colour can be found and named, laid over a space that is not regular. Munsell's value scale and the Natural Colour System's opponent quadrants are two different answers to the same question, and neither is a colour space.

Named by 6 essays across 3 fields — each of them below, with the objects they name alongside it.

Three lightness scales, seventy years apart. Munsell value, CIELAB's L* and CIECAM16's J against luminance, all rescaled to run 0 to 100. Each is somebody's answer to how evenly spaced lightness steps map onto light. They put the midpoint of the scale at 19.8%, 18.4% and 28.0% of the white's luminance respectively — close enough to be three measurements of one thing, far enough apart to be three measurements rather than one restated twice.

Colour by catalogue

A colour order system arranges physical samples on a regular lattice so a person can find one and name it. The space it samples is not regular, and everything interesting about such systems is what happens at that mismatch.

matching · Gamut A named ink, and the closest four-colour build of it. The ink is one pigment chosen for its own spectrum; the four-colour build is three chosen for everything. The four-colour build reaches it to ΔE00 = 0.37 under D50 and drifts to 4.46 under a tungsten lamp, because the match is metameric — the two curves cross 4 times rather than coinciding anywhere.

A brand colour is an ink

A named colour is a jar of pigment with a spectrum, and a four-colour build of it is three inks arranged to integrate to the same three numbers. Of 156 constructed single-pigment inks, 15 can be matched at all — and those fifteen drift by a median of 3.8 colour differences under a tungsten lamp, because the match was never a match.

applied · Delivery The eleven basic colour terms, at their quoted centroids. Each patch is the CIELAB centroid quoted for that term, converted to a stimulus and drawn — except blue, whose focal colour is outside the sRGB gamut and is therefore hatched rather than clipped, which is the rule for an unreachable colour everywhere else and applies here too. The centroids are rounded to 5 units in each coordinate, and moving them by that much either way leaves the same term outside.

A colour has a name

Every quantity here is a number, and the question a reader arrives with is what colour something is called. The eleven basic terms of English divide the space into territories that differ by a factor of five, the metric accounts for fifteen per cent of that, and one of the eleven focal colours cannot be shown on this page at all.

brain · Appearance A colour-order system's chips, sorted by what they would be called. A regular lattice in lightness, chroma and hue — the idealisation of a swatch book, and regular by construction because a person has to be able to find a page. Named, it comes apart: 1320 chips inside the gamut divide into 198 for grey and 66 for blue. And 22 per cent of one-step moves in the lattice change the name, so a page of a swatch book is not a page of a vocabulary.

A catalogue is not a vocabulary

A colour order system is a regular lattice, because a person has to be able to find a page. Sorted by what its chips would be called, that lattice comes apart into piles differing by a factor of three — and a fifth of all one-step moves in it change the name.

matching · Gamut How much of the gamut changes name, and what changed it. The eleven basic terms are quoted as centroids in CIELAB, and a colour is named by which one it is nearest. Two things nobody records decide the answer. Changing the distance function renames 20.5 per cent of the displayable gamut. Changing the room — the same colours, the same words, a different surround, through the appearance model — renames up to 26.8 per cent. The centroids were measured in one viewing condition and are applied here in every essay as though a name were a region of a space with no room in it.

A name moves with the room

Eleven basic colour terms are quoted as centroids in CIELAB and a colour is named by which one it is nearest. Two things nobody records decide the answer — which distance function is used, which renames a fifth of the displayable gamut, and which room the colour is in, which renames more than a quarter of it.

brain · Appearance How much of what a display can show each name owns. Every point on a 5-unit CIELAB lattice inside the sRGB gamut is given to its nearest centroid under ΔE00, and the shares counted. They run from 21.1 per cent for purple to 4.6 for blue, a factor of 4.6. The three terms that carry no chroma at all — black, grey and white — hold 20 per cent between them. A share here is a statement about the names and about the gamut they are counted over, and the gamut is sRGB.

A name in the model's own words

The eleven basic colour terms move when the room does, and the obvious objection is that they were being measured in a space with no room in it. Quoting them in an appearance model's own coordinates instead does not shrink the renaming — it grows it by four per cent — and the space alone renames an eighth of the gamut with the room held still.

brain · Appearance

Named alongside it

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

CIELABNamingBasic colour termsΔECategorical perceptionGamutPerceptual uniformitySpecificationCIECAM16Colour appearanceIndividual variationLightness

All concepts