[6a3a178] | 1 | import { epsilon, kappa, wd50X, wd50Y, wd50Z, matrix } from './util';
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| 2 |
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| 3 | /* Convert between Lab and XYZ
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| 4 | /* ========================================================================== */
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| 5 |
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| 6 | export function lab2xyz(labL, labA, labB) {
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| 7 | // compute f, starting with the luminance-related term
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| 8 | const f2 = (labL + 16) / 116;
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| 9 | const f1 = labA / 500 + f2;
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| 10 | const f3 = f2 - labB / 200;
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| 11 |
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| 12 | // compute pre-scaled XYZ
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| 13 | const [ initX, initY, initZ ] = [
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| 14 | Math.pow(f1, 3) > epsilon ? Math.pow(f1, 3) : (116 * f1 - 16) / kappa,
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| 15 | labL > kappa * epsilon ? Math.pow((labL + 16) / 116, 3) : labL / kappa,
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| 16 | Math.pow(f3, 3) > epsilon ? Math.pow(f3, 3) : (116 * f3 - 16) / kappa
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| 17 | ];
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| 18 |
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| 19 | const [ xyzX, xyzY, xyzZ ] = matrix(
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| 20 | // compute XYZ by scaling pre-scaled XYZ by reference white
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| 21 | [ initX * wd50X, initY * wd50Y, initZ * wd50Z ],
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| 22 | // calculate D65 XYZ from D50 XYZ
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| 23 | [
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| 24 | [ 0.9555766, -0.0230393, 0.0631636],
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| 25 | [-0.0282895, 1.0099416, 0.0210077],
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| 26 | [ 0.0122982, -0.0204830, 1.3299098]
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| 27 | ]
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| 28 | );
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| 29 |
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| 30 | return [ xyzX, xyzY, xyzZ ];
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| 31 | }
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| 32 |
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| 33 | export function xyz2lab(xyzX, xyzY, xyzZ) {
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| 34 | // calculate D50 XYZ from D65 XYZ
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| 35 | const [ d50X, d50Y, d50Z ] = matrix([ xyzX, xyzY, xyzZ ], [
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| 36 | [ 1.0478112, 0.0228866, -0.0501270],
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| 37 | [ 0.0295424, 0.9904844, -0.0170491],
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| 38 | [-0.0092345, 0.0150436, 0.7521316]
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| 39 | ]);
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| 40 |
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| 41 | // calculate f
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| 42 | const [ f1, f2, f3 ] = [
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| 43 | d50X / wd50X,
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| 44 | d50Y / wd50Y,
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| 45 | d50Z / wd50Z
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| 46 | ].map(
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| 47 | value => value > epsilon ? Math.cbrt(value) : (kappa * value + 16) / 116
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| 48 | );
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| 49 |
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| 50 | const [ labL, labA, labB ] = [
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| 51 | 116 * f2 - 16,
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| 52 | 500 * (f1 - f2),
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| 53 | 200 * (f2 - f3)
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| 54 | ];
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| 55 |
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| 56 | return [ labL, labA, labB ];
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| 57 | }
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| 58 |
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| 59 | /*
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| 60 |
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| 61 | References
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| 62 | ----------
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| 63 |
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| 64 | - https://www.w3.org/TR/css-color-4/#rgb-to-lab
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| 65 | - https://www.w3.org/TR/css-color-4/#color-conversion-code
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| 66 | - https://www.easyrgb.com/en/math.php
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| 67 |
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| 68 | /* ========================================================================== */
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