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/**
* @preserve
* Copyright 2015-2018 Igor Bezkrovnyi
* All rights reserved. (MIT Licensed)
*
* ciede2000.ts - part of Image Quantization Library
*/
import { AbstractDistanceCalculator } from './distanceCalculator';
import { rgb2lab } from '../conversion/rgb2lab';
import { degrees2radians, inRange0to255 } from '../utils/arithmetic';
/**
* CIEDE2000 algorithm - Adapted from Sharma et al's MATLAB implementation at
* http://www.ece.rochester.edu/~gsharma/ciede2000/
*/
export class CIEDE2000 extends AbstractDistanceCalculator {
/**
* Weight in distance: 0.25
* Max DeltaE: 100
* Max DeltaA: 255
*/
private static readonly _kA = (0.25 * 100) / 255;
private static readonly _pow25to7 = 25 ** 7;
private static readonly _deg360InRad = degrees2radians(360);
private static readonly _deg180InRad = degrees2radians(180);
private static readonly _deg30InRad = degrees2radians(30);
private static readonly _deg6InRad = degrees2radians(6);
private static readonly _deg63InRad = degrees2radians(63);
private static readonly _deg275InRad = degrees2radians(275);
private static readonly _deg25InRad = degrees2radians(25);
protected _setDefaults() {}
private static _calculatehp(b: number, ap: number) {
const hp = Math.atan2(b, ap);
if (hp >= 0) return hp;
return hp + CIEDE2000._deg360InRad;
}
private static _calculateRT(ahp: number, aCp: number) {
const aCp_to_7 = aCp ** 7.0;
const R_C = 2.0 * Math.sqrt(aCp_to_7 / (aCp_to_7 + CIEDE2000._pow25to7)); // 25^7
const delta_theta =
CIEDE2000._deg30InRad *
Math.exp(
-(((ahp - CIEDE2000._deg275InRad) / CIEDE2000._deg25InRad) ** 2.0),
);
return -Math.sin(2.0 * delta_theta) * R_C;
}
private static _calculateT(ahp: number) {
return (
1.0 -
0.17 * Math.cos(ahp - CIEDE2000._deg30InRad) +
0.24 * Math.cos(ahp * 2.0) +
0.32 * Math.cos(ahp * 3.0 + CIEDE2000._deg6InRad) -
0.2 * Math.cos(ahp * 4.0 - CIEDE2000._deg63InRad)
);
}
private static _calculate_ahp(
C1pC2p: number,
h_bar: number,
h1p: number,
h2p: number,
) {
const hpSum = h1p + h2p;
if (C1pC2p === 0) return hpSum;
if (h_bar <= CIEDE2000._deg180InRad) return hpSum / 2.0;
if (hpSum < CIEDE2000._deg360InRad) {
return (hpSum + CIEDE2000._deg360InRad) / 2.0;
}
return (hpSum - CIEDE2000._deg360InRad) / 2.0;
}
private static _calculate_dHp(
C1pC2p: number,
h_bar: number,
h2p: number,
h1p: number,
) {
let dhp;
if (C1pC2p === 0) {
dhp = 0;
} else if (h_bar <= CIEDE2000._deg180InRad) {
dhp = h2p - h1p;
} else if (h2p <= h1p) {
dhp = h2p - h1p + CIEDE2000._deg360InRad;
} else {
dhp = h2p - h1p - CIEDE2000._deg360InRad;
}
return 2.0 * Math.sqrt(C1pC2p) * Math.sin(dhp / 2.0);
}
calculateRaw(
r1: number,
g1: number,
b1: number,
a1: number,
r2: number,
g2: number,
b2: number,
a2: number,
) {
const lab1 = rgb2lab(
inRange0to255(r1 * this._whitePoint.r),
inRange0to255(g1 * this._whitePoint.g),
inRange0to255(b1 * this._whitePoint.b),
);
const lab2 = rgb2lab(
inRange0to255(r2 * this._whitePoint.r),
inRange0to255(g2 * this._whitePoint.g),
inRange0to255(b2 * this._whitePoint.b),
);
const dA = (a2 - a1) * this._whitePoint.a * CIEDE2000._kA;
const dE2 = this.calculateRawInLab(lab1, lab2);
return Math.sqrt(dE2 + dA * dA);
}
calculateRawInLab(
Lab1: { L: number; a: number; b: number },
Lab2: { L: number; a: number; b: number },
) {
// Get L,a,b values for color 1
const L1 = Lab1.L;
const a1 = Lab1.a;
const b1 = Lab1.b;
// Get L,a,b values for color 2
const L2 = Lab2.L;
const a2 = Lab2.a;
const b2 = Lab2.b;
// Calculate Cprime1, Cprime2, Cabbar
const C1 = Math.sqrt(a1 * a1 + b1 * b1);
const C2 = Math.sqrt(a2 * a2 + b2 * b2);
const pow_a_C1_C2_to_7 = ((C1 + C2) / 2.0) ** 7.0;
const G =
0.5 *
(1.0 -
Math.sqrt(pow_a_C1_C2_to_7 / (pow_a_C1_C2_to_7 + CIEDE2000._pow25to7))); // 25^7
const a1p = (1.0 + G) * a1;
const a2p = (1.0 + G) * a2;
const C1p = Math.sqrt(a1p * a1p + b1 * b1);
const C2p = Math.sqrt(a2p * a2p + b2 * b2);
const C1pC2p = C1p * C2p;
// Angles in Degree.
const h1p = CIEDE2000._calculatehp(b1, a1p);
const h2p = CIEDE2000._calculatehp(b2, a2p);
const h_bar = Math.abs(h1p - h2p);
const dLp = L2 - L1;
const dCp = C2p - C1p;
const dHp = CIEDE2000._calculate_dHp(C1pC2p, h_bar, h2p, h1p);
const ahp = CIEDE2000._calculate_ahp(C1pC2p, h_bar, h1p, h2p);
const T = CIEDE2000._calculateT(ahp);
const aCp = (C1p + C2p) / 2.0;
const aLp_minus_50_square = ((L1 + L2) / 2.0 - 50.0) ** 2.0;
const S_L =
1.0 +
(0.015 * aLp_minus_50_square) / Math.sqrt(20.0 + aLp_minus_50_square);
const S_C = 1.0 + 0.045 * aCp;
const S_H = 1.0 + 0.015 * T * aCp;
const R_T = CIEDE2000._calculateRT(ahp, aCp);
const dLpSL = dLp / S_L; // S_L * kL, where kL is 1.0
const dCpSC = dCp / S_C; // S_C * kC, where kC is 1.0
const dHpSH = dHp / S_H; // S_H * kH, where kH is 1.0
return dLpSL ** 2 + dCpSC ** 2 + dHpSH ** 2 + R_T * dCpSC * dHpSH;
}
}