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