NCS Colors

@urcolor/ncs teaches @urcolor/core the Natural Colour System notation, in both directions:

S 1050-Y90R
NCS S 2030-Y90R
4030-B50G
S 0500-N

It ships as a separate package. @urcolor/core never parses this notation on its own, so anyone who does not use NCS pays nothing for it.

Installation

bunnpmpnpm

bun add @urcolor/ncs

npm install @urcolor/ncs

pnpm add @urcolor/ncs

Usage

Parsing is not enabled by importing the package. Call registerNcsColor() once where the app boots:

import { Color } from "@urcolor/core";
import { registerNcsColor, toNcs } from "@urcolor/ncs";

registerNcsColor();

Color.parse("S 1050-Y90R");
toNcs(Color.parse("#eb7f7a")!); // "S 1050-Y90R"

The call returns an idempotent dispose function, so a test can register and unregister without leaking state into the next one:

const dispose = registerNcsColor();
dispose();
dispose(); // no-op

Registered parsers run after every built-in, so this package can neither shadow nor slow a standard notation.

Notation

Both prefixes are optional, ncs(…) wraps any form, and parsing is case-insensitive.

Form	Meaning
`S 1050-Y90R`	blackness 10, chromaticness 50, hue 90% from `Y` toward `R`
`1050-Y90R`	the same, prefix omitted
`NCS S 1050-Y90R`	the same, full prefix
`S 0580-Y`	an elementary hue, no second hue
`S 0500-N`	the neutral axis
`ncs(1050-Y90R)`	functional wrapper

Two rules return null rather than a wrong color. Blackness plus chromaticness must not exceed 100, since whiteness is the remainder. And a hue pair must name adjacent hues: the circle runs Y → R → B → G → Y, and NCS holds that no hue resembles both members of an opponent pair, so Y90R is a color while R90G and Y50B are not.

Accuracy

This is an approximation

NCS Colour AB holds the Natural Colour System as proprietary and publishes no open notation-to-sRGB mapping. The conversion is a model fitted against 2,031 published values, not a specification. Matching physical paint needs an official NCS fan deck.

NCS and Natural Colour System are trademarks of NCS Colour AB. This package ships a conversion, not the color system, and is affiliated with neither.

Measured against the full reference set: mean ΔE00 1.65, median 1.41, 95th percentile 3.76, worst 10.6, with 25 of 2,031 samples over 5.

Two weak spots are structural rather than incidental:

Very dark near-neutrals, around S 8505-*, where the color is nearly black and ΔE00 magnifies small absolute differences.
Chromaticness above about 75, where the model's chroma curve peaks and falls away, so two chromaticness values give the same lightness and chroma. No inverse can separate them, and toNcs() takes the lower reading.

Serialization

toNcs() returns exact two-digit values such as S 1347-Y83R, not snapped to the NCS standard sample grid. A result therefore round-trips through Color.parse() but does not necessarily name a real, orderable NCS sample. Snapping would require NCS Colour AB's copyrighted sample list and would move the color silently.

Colors outside what NCS expresses are clamped, so toNcs() always answers. Round-trip it when that matters:

import { deltaE } from "@urcolor/core";

const notation = toNcs(color);
const faithful = deltaE(color.toObject(), Color.parse(notation)!.toObject(), "2000") < 2;

Across a sweep of the whole notation space a round trip is mean ΔE00 0.19, 95th percentile 1.01, worst 6.17.

NCS Colors ​

Installation ​

Usage ​

Notation ​