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Filename : ciede2000.ts
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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;
  }
}