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Contents
import { epsilon, kappa, wd50X, wd50Y, wd50Z, matrix } from './util';
/* Convert between Lab and XYZ
/* ========================================================================== */
export function lab2xyz(labL, labA, labB) {
// compute f, starting with the luminance-related term
const f2 = (labL + 16) / 116;
const f1 = labA / 500 + f2;
const f3 = f2 - labB / 200;
// compute pre-scaled XYZ
const [ initX, initY, initZ ] = [
Math.pow(f1, 3) > epsilon ? Math.pow(f1, 3) : (116 * f1 - 16) / kappa,
labL > kappa * epsilon ? Math.pow((labL + 16) / 116, 3) : labL / kappa,
Math.pow(f3, 3) > epsilon ? Math.pow(f3, 3) : (116 * f3 - 16) / kappa
];
const [ xyzX, xyzY, xyzZ ] = matrix(
// compute XYZ by scaling pre-scaled XYZ by reference white
[ initX * wd50X, initY * wd50Y, initZ * wd50Z ],
// calculate D65 XYZ from D50 XYZ
[
[ 0.9555766, -0.0230393, 0.0631636],
[-0.0282895, 1.0099416, 0.0210077],
[ 0.0122982, -0.0204830, 1.3299098]
]
);
return [ xyzX, xyzY, xyzZ ];
}
export function xyz2lab(xyzX, xyzY, xyzZ) {
// calculate D50 XYZ from D65 XYZ
const [ d50X, d50Y, d50Z ] = matrix([ xyzX, xyzY, xyzZ ], [
[ 1.0478112, 0.0228866, -0.0501270],
[ 0.0295424, 0.9904844, -0.0170491],
[-0.0092345, 0.0150436, 0.7521316]
]);
// calculate f
const [ f1, f2, f3 ] = [
d50X / wd50X,
d50Y / wd50Y,
d50Z / wd50Z
].map(
value => value > epsilon ? Math.cbrt(value) : (kappa * value + 16) / 116
);
const [ labL, labA, labB ] = [
116 * f2 - 16,
500 * (f1 - f2),
200 * (f2 - f3)
];
return [ labL, labA, labB ];
}
/*
References
----------
- https://www.w3.org/TR/css-color-4/#rgb-to-lab
- https://www.w3.org/TR/css-color-4/#color-conversion-code
- https://www.easyrgb.com/en/math.php
/* ========================================================================== */
Version data entries
26 entries across 25 versions & 8 rubygems