Spectral.js

/*************************************************************************
 *  @license
 *
 *
 *  Copyright © 2019, 2024 Glenn Wilton
 *  O2 Creative Limited
 *  www.o2creative.co.nz
 *  support@o2creative.co.nz
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 *
 */
'use strict';

/* ============================================================================
 *  Spectral.js — spectral data and reflectance → XYZ/Lab integration
 * ============================================================================
 *
 *  This module is for working with COLOUR AS PHYSICS rather than colour as
 *  device numbers. If you are converting RGB → CMYK or applying an ICC
 *  profile, you don't need this file — use Profile / Transform instead.
 *
 *  You DO need this file when you have:
 *
 *    - A reflectance or transmittance spectrum from a spectrophotometer
 *      (i1Pro, X-Rite eXact, Konica Minolta CM-26d, Barbieri Spectro, ...).
 *      Most spectros report 36 or 31 reflectance values from 380-730 nm in
 *      10 nm steps, or 81 values in 5 nm steps.
 *
 *    - A spectral library (Pantone Live, ink/paint formulator output, NCS,
 *      Munsell book of color, the digitised IT8.7/4 / ECI2002 / TC1617 /
 *      GATCS targets used to build ICC profiles).
 *
 *    - A simulated illuminant and you want to know what a sample would look
 *      like under different lights ("metamerism check" — does this print
 *      match under D50 daylight AND under F11 store fluorescent?).
 *
 *
 *  WHAT'S IN THIS FILE
 *  ----------------------------------------------------------------------------
 *
 *   1. Illuminants[] — the relative spectral power distribution (SPD) of
 *      a few CIE standard light sources:
 *        A    Tungsten-filament,            ~2856 K
 *        C    Old "average daylight",       ~6774 K  (deprecated, kept for legacy targets)
 *        D50  ISO graphic-arts viewing,      5000 K  (the default for ICC)
 *        D55  Mid-morning/afternoon,         5500 K
 *        D65  Noon daylight,                 6504 K  (the default for sRGB)
 *
 *      Each is a curve S(λ) sampled at fixed nm steps, normalised so that
 *      the value at 560 nm ≈ 100. Add F-series (fluorescent) or LED SPDs
 *      here if you need them — same shape.
 *
 *   2. Observers[] — the CIE colour-matching functions x̄(λ), ȳ(λ), z̄(λ):
 *        2°   CIE 1931 standard observer  (most colour work)
 *        10°  CIE 1964 standard observer  (large-field work, paint, textiles)
 *
 *      These describe how the human eye's three cone types respond to each
 *      wavelength. They turn an SPD into a tristimulus (X, Y, Z) value.
 *
 *   3. The Spectral class with helpers and the integration `calculateXYZ()`
 *      which turns reflectance + illuminant + observer into XYZ. The
 *      returned XYZ already carries the illuminant's whitePoint so passing
 *      it to convert.XYZ2Lab() (or piping it through a Transform) gives
 *      Lab measured under that illuminant.
 *
 *
 *  THE MATH (calculateXYZ)
 *  ----------------------------------------------------------------------------
 *
 *      X = k · Σ S(λ) · R(λ) · x̄(λ)
 *      Y = k · Σ S(λ) · R(λ) · ȳ(λ)
 *      Z = k · Σ S(λ) · R(λ) · z̄(λ)
 *
 *      k = 100 / Σ S(λ) · ȳ(λ)
 *
 *      where  S(λ) = illuminant SPD                  (Illuminants[].data)
 *             R(λ) = sample reflectance              (your spectrum.data)
 *             x̄ ȳ z̄ = observer matching functions   (Observers[].X/Y/Z)
 *
 *  The Δλ that should appear inside each sum cancels in the ratio because
 *  the same step is used in numerator and denominator, so it is omitted from
 *  the loop. Wavelengths where the spectrum's grid doesn't line up with the
 *  illuminant's or observer's grid are linearly interpolated.
 *
 *
 *  TYPICAL USAGE
 *  ----------------------------------------------------------------------------
 *
 *      var Spectral = require('jscolorengine').Spectral;
 *      var s = new Spectral();
 *
 *      // 36 reflectance values from a spectro, 380-730 nm @ 10 nm
 *      var swatch = s.toSpectral(380, 730, [0.05, 0.04, 0.04, ...], 10);
 *
 *      var d50 = s.getIlluminant('D50');
 *      var obs2 = s.getObserver('2');
 *
 *      var xyz   = s.calculateXYZ(swatch, d50, obs2);  // {type, X, Y, Z, whitePoint}
 *      var lab   = convert.XYZ2Lab(xyz);                // Lab under D50/2°
 *
 *      // Same swatch under D65/10° — for a metamerism check
 *      var labD65 = convert.XYZ2Lab(
 *          s.calculateXYZ(swatch, s.getIlluminant('D65'), s.getObserver('10'))
 *      );
 *      var dE = convert.deltaE76(lab, labD65);   // how different they look
 *
 *
 *  PERFORMANCE NOTE
 *  ----------------------------------------------------------------------------
 *
 *  This is an ACCURACY-PATH module (see Transform.js USAGE GUIDE for the
 *  same distinction). calculateXYZ is typically called once per spectro
 *  reading — tens to thousands of times in a profile build, NOT millions of
 *  times per image. The loop is straightforward and not micro-optimised;
 *  if you find yourself calling it per pixel, you are doing the wrong thing
 *  — pre-build a LUT instead.
 *
 *
 *  REFERENCES
 *  ----------------------------------------------------------------------------
 *
 *   CIE 015:2018  Colorimetry, 4th edition  (the canonical reference)
 *   ASTM E308     Standard practice for computing colors of objects
 *   Wikipedia: "CIE 1931 color space", "Standard illuminant", "Tristimulus values"
 *   Bruce Lindbloom: http://www.brucelindbloom.com/  (excellent practical tables)
 *   The Munsell Color Science Lab spectral data archives
 *
 * ============================================================================
 */

var convert = require('./convert');

/* ----------------------------------------------------------------------------
 *  Illuminants — CIE Standard Illuminant relative spectral power distributions
 *
 *  Schema for each entry:
 *    name        Short name used as a key in getIlluminant('D50') etc.
 *    description Human-readable note.
 *    isDefault   (D50 only) flag for "use this if the caller didn't pick one".
 *    startnm     First wavelength in `data`, in nanometres.
 *    endnm       Last wavelength in `data`, in nanometres.
 *    step        Nm spacing between consecutive `data` values.
 *    range       Legacy scale denominator (~max(data)); not used by calculateXYZ.
 *    temp        Correlated colour temperature in Kelvin.
 *    whitePoint  Reference XYZ whitepoint object from convert.js. The XYZ
 *                returned by calculateXYZ() inherits this so downstream
 *                Lab conversion uses the matching whitepoint.
 *    data        Relative SPD samples, normalised so data[wavelength=560nm] ≈ 100.
 *
 *  Coverage and step size matter: an integration over 380-730 nm @ 5 nm is
 *  the de-facto industry standard (matches typical spectro output). Wider
 *  range / smaller step costs nothing per call here and improves accuracy at
 *  the edges of the visible band.
 * ---------------------------------------------------------------------------- */

var Illuminants =  [
   {
        name: 'A',
        description: '# CIE standard Illuminant A, a typical tungsten-filament light with relative spectral power distribution of 2856K, at 1nm resolution',
        startnm: 300,
        endnm: 830,
        step: 1,
        range: 1000,
        temp: 2856.1,
        whitePoint: convert.a,
        data: [
            0.930483, 0.967643, 1.00597, 1.04549, 1.08623, 1.12821, 1.17147, 1.21602, 1.26188, 1.3091, 1.35769, 1.40768, 1.4591, 1.51198, 1.56633, 1.62219, 1.67959, 1.73855, 1.7991, 1.86127, 1.92508, 1.99057, 2.05776, 2.12667, 2.19734, 2.2698, 2.34406, 2.42017, 2.49814, 2.57801, 2.65981, 2.74355, 2.82928, 2.91701, 3.00678, 3.09861, 3.19253, 3.28857, 3.38676, 3.48712, 3.58968, 3.69447, 3.80152, 3.91085, 4.0225, 4.13648, 4.25282, 4.37156, 4.49272, 4.61631, 4.74238, 4.87095, 5.00204, 5.13568, 5.27189, 5.4107, 5.55213, 5.69622, 5.84298, 5.99244, 6.14462, 6.29955, 6.45724, 6.61774, 6.78105, 6.9472, 7.11621, 7.28811, 7.46292, 7.64066, 7.82135, 8.00501, 8.19167, 8.38134, 8.57404, 8.7698, 8.96864, 9.17056, 9.37561, 9.58378, 9.7951, 10.0096, 10.2273, 10.4481, 10.6722, 10.8996, 11.1302, 11.364, 11.6012, 11.8416, 12.0853, 12.3324, 12.5828, 12.8366, 13.0938, 13.3543, 13.6182, 13.8855, 14.1563, 14.4304, 14.708, 14.9891, 15.2736, 15.5616, 15.853, 16.148, 16.4464, 16.7484, 17.0538, 17.3628, 17.6753, 17.9913, 18.3108, 18.6339, 18.9605, 19.2907, 19.6244, 19.9617, 20.3026, 20.647, 20.995, 21.3465, 21.7016, 22.0603, 22.4225, 22.7883, 23.1577, 23.5307, 23.9072, 24.2873, 24.6709, 25.0581, 25.4489, 25.8432, 26.2411, 26.6425, 27.0475, 27.456, 27.8681, 28.2836, 28.7027, 29.1253, 29.5515, 29.9811, 30.4142, 30.8508, 31.2909, 31.7345, 32.1815, 32.632, 33.0859, 33.5432, 34.004, 34.4682, 34.9358, 35.4068, 35.8811, 36.3588, 36.8399, 37.3243, 37.8121, 38.3031, 38.7975, 39.2951, 39.796, 40.3002, 40.8076, 41.3182, 41.832, 42.3491, 42.8693, 43.3926, 43.9192, 44.4488, 44.9816, 45.5174, 46.0563, 46.5983, 47.1433, 47.6913, 48.2423, 48.7963, 49.3533, 49.9132, 50.476, 51.0418, 51.6104, 52.1818, 52.7561, 53.3332, 53.9132, 54.4958, 55.0813, 55.6694, 56.2603, 56.8539, 57.4501, 58.0489, 58.6504, 59.2545, 59.8611, 60.4703, 61.082, 61.6962, 62.3128, 62.932, 63.5535, 64.1775, 64.8038, 65.4325, 66.0635, 66.6968, 67.3324, 67.9702, 68.6102, 69.2525, 69.8969, 70.5435, 71.1922, 71.843, 72.4959, 73.1508, 73.8077, 74.4666, 75.1275, 75.7903, 76.4551, 77.1217, 77.7902, 78.4605, 79.1326, 79.8065, 80.4821, 81.1595, 81.8386, 82.5193, 83.2017, 83.8856, 84.5712, 85.2584, 85.947, 86.6372, 87.3288, 88.0219, 88.7165, 89.4124, 90.1097, 90.8083, 91.5082, 92.2095, 92.912, 93.6157, 94.3206, 95.0267, 95.7339, 96.4423, 97.1518, 97.8623, 98.5739, 99.2864, 100, 100.715, 101.43, 102.146, 102.864, 103.582, 104.301, 105.02, 105.741, 106.462, 107.184, 107.906, 108.63, 109.354, 110.078, 110.803, 111.529, 112.255, 112.982, 113.709, 114.436, 115.164, 115.893, 116.622, 117.351, 118.08, 118.81, 119.54, 120.27, 121.001, 121.731, 122.462, 123.193, 123.924, 124.655, 125.386, 126.118, 126.849, 127.58, 128.312, 129.043, 129.774, 130.505, 131.236, 131.966, 132.697, 133.427, 134.157, 134.887, 135.617, 136.346, 137.075, 137.804, 138.532, 139.26, 139.988, 140.715, 141.441, 142.167, 142.893, 143.618, 144.343, 145.067, 145.79, 146.513, 147.235, 147.957, 148.678, 149.398, 150.117, 150.836, 151.554, 152.271, 152.988, 153.704, 154.418, 155.132, 155.845, 156.558, 157.269, 157.979, 158.689, 159.397, 160.104, 160.811, 161.516, 162.221, 162.924, 163.626, 164.327, 165.028, 165.726, 166.424, 167.121, 167.816, 168.51, 169.203, 169.895, 170.586, 171.275, 171.963, 172.65, 173.335, 174.019, 174.702, 175.383, 176.063, 176.741, 177.419, 178.094, 178.769, 179.441, 180.113, 180.783, 181.451, 182.118, 182.783, 183.447, 184.109, 184.77, 185.429, 186.087, 186.743, 187.397, 188.05, 188.701, 189.35, 189.998, 190.644, 191.288, 191.931, 192.572, 193.211, 193.849, 194.484, 195.118, 195.75, 196.381, 197.009, 197.636, 198.261, 198.884, 199.506, 200.125, 200.743, 201.359, 201.972, 202.584, 203.195, 203.803, 204.409, 205.013, 205.616, 206.216, 206.815, 207.411, 208.006, 208.599, 209.189, 209.778, 210.365, 210.949, 211.532, 212.112, 212.691, 213.268, 213.842, 214.415, 214.985, 215.553, 216.12, 216.684, 217.246, 217.806, 218.364, 218.92, 219.473, 220.025, 220.574, 221.122, 221.667, 222.21, 222.751, 223.29, 223.826, 224.361, 224.893, 225.423, 225.951, 226.477, 227, 227.522, 228.041, 228.558, 229.073, 229.585, 230.096, 230.604, 231.11, 231.614, 232.115, 232.615, 233.112, 233.606, 234.099, 234.589, 235.078, 235.564, 236.047, 236.529, 237.008, 237.485, 237.959, 238.432, 238.902, 239.37, 239.836, 240.299, 240.76, 241.219, 241.675, 242.13, 242.582, 243.031, 243.479, 243.924, 244.367, 244.808, 245.246, 245.682, 246.116, 246.548, 246.977, 247.404, 247.829, 248.251, 248.671, 249.089, 249.505, 249.918, 250.329, 250.738, 251.144, 251.548, 251.95, 252.35, 252.747, 253.142, 253.535, 253.925, 254.314, 254.7, 255.083, 255.465, 255.844, 256.221, 256.595, 256.968, 257.338, 257.706, 258.071, 258.434, 258.795, 259.154, 259.511, 259.865, 260.217, 260.567, 260.914, 261.259, 261.602
        ]
   },
   {
        name: 'C',
        description: 'CIE deprecated standard Illuminant C, approximately 6774K, at 5nm resolution',
        startnm: 380,
        endnm: 780,
        step: 5,
        range: 1000,
        temp: 6769.2,
        whitePoint: convert.c,
        data: [
            33, 39.92, 47.4, 55.17, 63.3, 71.81, 80.6, 89.53, 98.1, 105.8, 112.4, 117.75, 121.5, 123.45, 124, 123.6, 123.1, 123.3, 123.8, 124.09, 123.9, 122.92, 120.7, 116.9, 112.1, 106.98, 102.3, 98.81, 96.9, 96.78, 98, 99.94, 102.1, 103.95, 105.2, 105.67, 105.3, 104.11, 102.3, 100.15, 97.8, 95.43, 93.2, 91.22, 89.7, 88.83, 88.4, 88.19, 88.1, 88.06, 88, 87.86, 87.8, 87.99, 88.2, 88.2, 87.9, 87.22, 86.3, 85.3, 84, 82.21, 80.2, 78.24, 76.3, 74.36, 72.4, 70.4, 68.3, 66.3, 64.4, 62.8, 61.5, 60.2, 59.2, 58.5, 58.1, 58, 58.2, 58.5, 59.1
        ]
   },
   {
        name: 'D50',
        description: 'CIE standard D50 illuminator, approximating light at the horizon at 5nm resolution',
        isDefault: true,
        startnm: 380,
        endnm: 780,
        step: 5,
        range: 1000,
        temp: 5000,
        whitePoint: convert.d50,
        data: [
            24.5, 27.2, 29.8, 39.6, 49.3, 52.9, 56.5, 58.3, 60, 58.9, 57.8, 66.3, 74.8, 81, 87.2, 88.9, 90.6, 91, 91.4, 93.3, 95.2, 93.6, 92, 93.9, 95.7, 96.2, 96.6, 96.9, 97.1, 99.6, 102.1, 101.5, 100.8, 101.6, 102.3, 101.2, 100, 98.9, 97.7, 98.3, 98.9, 96.2, 93.5, 95.6, 97.7, 98.5, 99.3, 99.2, 99, 97.4, 95.7, 97.3, 98.8, 97.3, 95.7, 97, 98.2, 100.6, 103, 101.1, 99.1, 93.3, 87.4, 89.5, 91.6, 92.3, 92.9, 84.9, 76.8, 81.7, 86.6, 89.6, 92.6, 85.4, 78.2, 68, 57.7, 70.3, 82.9, 80.6, 78.3
        ]
   },
   {
        name: 'D55',
        description: 'CIE standard Illuminant D55, mid-morning/mid-afternoon daylight, at 5nm resolution',
        startnm: 380,
        endnm: 780,
        step: 5,
        range: 1000,
        temp: 5500,
        whitePoint: convert.d55,
        data: [
            32.58, 35.34, 38.09, 49.52, 60.95, 64.75, 68.55, 70.07, 71.58, 69.75, 67.91, 76.76, 85.61, 91.8, 97.99, 99.23, 100.46, 100.19, 99.91, 101.33, 102.74, 100.41, 98.08, 99.38, 100.68, 100.69, 100.7, 100.34, 99.99, 102.1, 104.21, 103.16, 102.1, 102.53, 102.97, 101.48, 100, 98.61, 97.22, 97.48, 97.75, 94.59, 91.43, 92.93, 94.42, 94.78, 95.14, 94.68, 94.22, 92.33, 90.45, 91.39, 92.33, 90.59, 88.85, 89.59, 90.32, 92.13, 93.95, 91.95, 89.96, 84.82, 79.68, 81.26, 82.84, 83.84, 84.84, 77.54, 70.24, 74.77, 79.3, 82.15, 84.99, 78.44, 71.88, 62.34, 52.79, 64.36, 75.93, 73.87, 71.82
        ]
   },
   {
        name: 'D65',
        description: 'CIE standard Illuminant D65, at 5nm resolution',
        startnm: 300,
        endnm: 830,
        step: 5,
        range: 1000,
        temp: 6500,
        whitePoint: convert.d65,
        data: [
            0.0341, 1.6643, 3.2945, 11.7652, 20.236, 28.6447, 37.0535, 38.5011, 39.9488, 42.4302, 44.9117, 45.775, 46.6383, 49.3637, 52.0891, 51.0323, 49.9755, 52.3118, 54.6482, 68.7015, 82.7549, 87.1204, 91.486, 92.4589, 93.4318, 90.057, 86.6823, 95.7736, 104.865, 110.936, 117.008, 117.41, 117.812, 116.336, 114.861, 115.392, 115.923, 112.367, 108.811, 109.082, 109.354, 108.578, 107.802, 106.296, 104.79, 106.239, 107.689, 106.047, 104.405, 104.225, 104.046, 102.023, 100, 98.1671, 96.3342, 96.0611, 95.788, 92.2368, 88.6856, 89.3459, 90.0062, 89.8026, 89.5991, 88.6489, 87.6987, 85.4936, 83.2886, 83.4939, 83.6992, 81.863, 80.0268, 80.1207, 80.2146, 81.2462, 82.2778, 80.281, 78.2842, 74.0027, 69.7213, 70.6652, 71.6091, 72.979, 74.349, 67.9765, 61.604, 65.7448, 69.8856, 72.4863, 75.087, 69.3398, 63.5927, 55.0054, 46.4182, 56.6118, 66.8054, 65.0941, 63.3828, 63.8434, 64.304, 61.8779, 59.4519, 55.7054, 51.959, 54.6998, 57.4406, 58.8765, 60.3125
        ]
   }
];

/* ----------------------------------------------------------------------------
 *  Observers — CIE Standard Observer colour-matching functions x̄(λ), ȳ(λ), z̄(λ)
 *
 *  The colour-matching functions describe how the eye's three cone responses
 *  combine to produce tristimulus (X, Y, Z) sensations for monochromatic
 *  light at wavelength λ. Multiplying an SPD by these and summing gives XYZ.
 *
 *  Two standard observers are provided:
 *    '2'   CIE 1931  2°  — small visual field. The historical default and
 *                          the right choice for most ICC / graphic-arts work,
 *                          colour pickers, soft proofing, etc.
 *    '10'  CIE 1964  10° — large visual field. Used in paint, textiles, and
 *                          industrial colour matching where samples subtend
 *                          a larger angle. CRF / ΔE numbers can differ
 *                          noticeably from 2° on saturated reds and blues.
 *
 *  Schema for each entry:
 *    name        '2' or '10' (used as a key in getObserver('2') etc.)
 *    description Human-readable note.
 *    isDefault   ('2' only) flag for "use this if the caller didn't pick one".
 *    startnm     First wavelength in X/Y/Z, in nanometres.
 *    endnm       Last  wavelength in X/Y/Z, in nanometres.
 *    step        Nm spacing between consecutive samples (1 nm here).
 *    range       Legacy scale denominator (~max value); not used by calculateXYZ.
 *    X, Y, Z     The three colour-matching curves x̄(λ), ȳ(λ), z̄(λ),
 *                each as an array of length (endnm - startnm) / step + 1.
 *
 *  Note: Y(λ) (=ȳ) is by definition the photopic luminous efficiency
 *  function V(λ), so a sum of S(λ)·Y(λ) is proportional to luminance — that
 *  is why the k normaliser in calculateXYZ uses only Y.
 * ---------------------------------------------------------------------------- */

var Observers = [
    {
        name: '2',
        description: 'CIE 1931 standard 2° observer tristimulus response values',
        isDefault: true,
        startnm: 360,
        endnm: 830,
        step: 1,
        range: 1000,
        X: [
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    {
        name: '10',
        description: 'CIE 1964 10° standard observer tristimulus response values',
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        endnm: 830,
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        range: 1000,
        X: [
            0.000000122,0.000000185,0.000000279,0.000000417,0.000000621,0.000000919,0.000001352,0.000001977,0.000002872,0.00000415,0.000005959,0.000008506,0.000012069,0.000017023,0.000023868,0.000033266,0.000046087,0.000063472,0.000086892,0.000118246,0.000159952,0.00021508,0.00028749,0.00038199,0.00050455,0.00066244,0.0008645,0.0011215,0.00144616,0.00185359,0.0023616,0.0029906,0.0037645,0.0047102,0.0058581,0.0072423,0.0088996,0.0108709,0.0131989,0.0159292,0.0191097,0.022788,0.027011,0.031829,0.037278,0.0434,0.050223,0.057764,0.066038,0.075033,0.084736,0.095041,0.105836,0.117066,0.128682,0.140638,0.152893,0.165416,0.178191,0.191214,0.204492,0.21765,0.230267,0.242311,0.253793,0.264737,0.275195,0.285301,0.295143,0.304869,0.314679,0.324355,0.33357,0.342243,0.350312,0.357719,0.364482,0.370493,0.375727,0.380158,0.383734,0.386327,0.387858,0.388396,0.387978,0.386726,0.384696,0.382006,0.378709,0.374915,0.370702,0.366089,0.361045,0.355518,0.349486,0.342957,0.335893,0.328284,0.32015,0.311475,0.302273,0.292858,0.283502,0.274044,0.264263,0.254085,0.243392,0.232187,0.220488,0.208198,0.195618,0.183034,0.170222,0.157348,0.14465,0.132349,0.120584,0.109456,0.099042,0.089388,0.080507,0.072034,0.06371,0.055694,0.048117,0.041072,0.034642,0.028896,0.023876,0.019628,0.016172,0.0133,0.010759,0.008542,0.006661,0.005132,0.003982,0.003239,0.002934,0.003114,0.003816,0.005095,0.006936,0.009299,0.012147,0.015444,0.019156,0.02325,0.02769,0.032444,0.037465,0.042956,0.049114,0.05592,0.063349,0.071358,0.079901,0.088909,0.098293,0.107949,0.117749,0.127839,0.13845,0.149516,0.161041,0.172953,0.185209,0.197755,0.210538,0.22346,0.236491,0.249633,0.262972,0.276515,0.290269,0.304213,0.318361,0.332705,0.347232,0.361926,0.376772,0.391683,0.406594,0.421539,0.436517,0.451584,0.466782,0.482147,0.497738,0.513606,0.529826,0.54644,0.563426,0.580726,0.59829,0.616053,0.633948,0.651901,0.669824,0.687632,0.705224,0.722773,0.740483,0.758273,0.776083,0.793832,0.811436,0.828822,0.845879,0.862525,0.878655,0.894208,0.909206,0.923672,0.937638,0.951162,0.964283,0.977068,0.98959,1.002,1.014,1.026,1.039,1.051,1.063,1.074,1.085,1.095,1.104,1.112,1.119,1.124,1.128,1.131,1.133,1.134,1.134,1.133,1.131,1.128,1.124,1.119,1.113,1.106,1.098,1.089,1.079,1.068,1.057,1.044,1.03,1.016,1.001,0.98479,0.96808,0.95074,0.9328,0.91434,0.89539,0.87603,0.856297,0.83635,0.81629,0.79605,0.77561,0.75493,0.73399,0.71278,0.69129,0.66952,0.647467,0.62511,0.60252,0.57989,0.55737,0.53511,0.51324,0.49186,0.47108,0.45096,0.431567,0.41287,0.39475,0.37721,0.36019,0.34369,0.32769,0.31217,0.29711,0.2825,0.268329,0.25459,0.2413,0.22848,0.21614,0.2043,0.19295,0.18211,0.17177,0.16192,0.152568,0.14367,0.1352,0.12713,0.11948,0.11221,0.10531,0.098786,0.09261,0.086773,0.0812606,0.076048,0.071114,0.066454,0.062062,0.05793,0.05405,0.050412,0.047006,0.043823,0.0408508,0.038072,0.035468,0.033031,0.030753,0.028623,0.026635,0.024781,0.023052,0.021441,0.0199413,0.018544,0.017241,0.016027,0.014896,0.013842,0.012862,0.011949,0.0111,0.010311,0.00957688,0.008894,0.0082581,0.0076664,0.0071163,0.0066052,0.0061306,0.0056903,0.0052819,0.0049033,0.00455263,0.0042275,0.0039258,0.0036457,0.0033859,0.0031447,0.0029208,0.002713,0.0025202,0.0023411,0.00217496,0.0020206,0.0018773,0.0017441,0.0016205,0.0015057,0.0013992,0.0013004,0.0012087,0.0011236,0.00104476,0.00097156,0.0009036,0.00084048,0.00078187,0.00072745,0.0006769,0.00062996,0.00058637,0.00054587,0.000508258,0.0004733,0.0004408,0.00041058,0.00038249,0.00035638,0.00033211,0.00030955,0.00028858,0.00026909,0.000250969,0.00023413,0.00021847,0.00020391,0.00019035,0.00017773,0.00016597,0.00015502,0.0001448,0.00013528,0.00012639,0.0001181,0.00011037,0.00010315,0.000096427,0.000090151,0.000084294,0.00007883,0.000073729,0.000068969,0.000064526,0.000060376,0.0000565,0.00005288,0.000049498,0.000046339,0.000043389,0.000040634,0.00003806,0.000035657,0.000033412,0.000031315,0.000029355,0.000027524,0.000025811,0.000024209,0.000022711,0.000021308,0.000019994,0.000018764,0.000017612,0.000016532,0.000015521,0.000014574,0.000013686,0.000012855,0.000012075,0.000011345,0.000010659,0.000010017,0.000009414,0.000008848,0.000008317,0.000007819,0.000007352,0.000006913,0.000006502,0.000006115,0.000005753,0.000005413,0.000005093,0.000004794,0.000004512,0.000004248,0.000004,0.000003767,0.000003548,0.000003342,0.000003148,0.000002966,0.000002795,0.000002634,0.000002483,0.000002341,0.000002208,0.000002082,0.000001964,0.000001852,0.000001746,0.000001647,0.000001553
        ],
        Y: [
            0.000000013,0.00000002,0.000000031,0.000000046,0.000000068,0.000000101,0.000000148,0.000000216,0.000000314,0.000000454,0.000000651,0.000000929,0.000001318,0.000001857,0.000002602,0.000003625,0.000005019,0.000006907,0.000009449,0.000012848,0.000017364,0.000023327,0.00003115,0.00004135,0.00005456,0.00007156,0.0000933,0.00012087,0.00015564,0.0001992,0.0002534,0.0003202,0.0004024,0.0005023,0.0006232,0.0007685,0.0009417,0.0011478,0.0013903,0.001674,0.0020044,0.002386,0.002822,0.003319,0.00388,0.004509,0.005209,0.005985,0.006833,0.007757,0.008756,0.009816,0.010918,0.012058,0.013237,0.014456,0.015717,0.017025,0.018399,0.019848,0.021391,0.022992,0.024598,0.026213,0.027841,0.029497,0.031195,0.032927,0.034738,0.036654,0.038676,0.040792,0.042946,0.045114,0.047333,0.049602,0.051934,0.054337,0.056822,0.059399,0.062077,0.064737,0.067285,0.069764,0.072218,0.074704,0.077272,0.079979,0.082874,0.086,0.089456,0.092947,0.096275,0.099535,0.102829,0.106256,0.109901,0.113835,0.118167,0.122932,0.128201,0.133457,0.138323,0.143042,0.147787,0.152761,0.158102,0.163941,0.170362,0.177425,0.18519,0.193025,0.200313,0.207156,0.213644,0.21994,0.22617,0.232467,0.239025,0.245997,0.253589,0.261876,0.270643,0.279645,0.288694,0.297665,0.306469,0.315035,0.323335,0.331366,0.339133,0.34786,0.358326,0.370001,0.382464,0.395379,0.408482,0.421588,0.434619,0.447601,0.460777,0.47434,0.4882,0.50234,0.51674,0.53136,0.54619,0.56118,0.57629,0.5915,0.606741,0.62215,0.63783,0.65371,0.66968,0.68566,0.70155,0.71723,0.73257,0.74746,0.761757,0.77534,0.78822,0.80046,0.81214,0.82333,0.83412,0.8446,0.85487,0.86504,0.875211,0.88537,0.89537,0.90515,0.91465,0.92381,0.93255,0.94081,0.94852,0.9556,0.961988,0.96754,0.97223,0.97617,0.97946,0.9822,0.98452,0.98652,0.98832,0.99002,0.991761,0.99353,0.99523,0.99677,0.99809,0.99911,0.99977,1,0.99971,0.99885,0.99734,0.99526,0.99274,0.98975,0.9863,0.98238,0.97798,0.97311,0.96774,0.96189,0.955552,0.948601,0.940981,0.932798,0.924158,0.915175,0.905954,0.896608,0.887249,0.877986,0.868934,0.860164,0.851519,0.842963,0.834393,0.825623,0.816764,0.807544,0.797947,0.787893,0.777405,0.76649,0.755309,0.743845,0.73219,0.720353,0.708281,0.696055,0.683621,0.671048,0.658341,0.645545,0.632718,0.619815,0.606887,0.593878,0.580781,0.567653,0.55449,0.541228,0.527963,0.514634,0.501363,0.488124,0.474935,0.461834,0.448823,0.435917,0.423153,0.410526,0.398057,0.385835,0.373951,0.362311,0.350863,0.339554,0.328309,0.317118,0.305936,0.294737,0.283493,0.272222,0.26099,0.249877,0.238946,0.228254,0.217853,0.20778,0.198072,0.188748,0.179828,0.171285,0.163059,0.155151,0.147535,0.140211,0.13317,0.1264,0.119892,0.11364,0.107633,0.10187,0.096347,0.091063,0.08601,0.081187,0.076583,0.072198,0.068024,0.064052,0.060281,0.056697,0.053292,0.050059,0.046998,0.044096,0.041345,0.0387507,0.0362978,0.0339832,0.0318004,0.0297395,0.0277918,0.0259551,0.0242263,0.0226017,0.0210779,0.0196505,0.0183153,0.0170686,0.0159051,0.0148183,0.0138008,0.0128495,0.0119607,0.0111303,0.0103555,0.0096332,0.0089599,0.0083324,0.0077488,0.0072046,0.0066975,0.0062251,0.005785,0.0053751,0.0049941,0.0046392,0.0043093,0.0040028,0.00371774,0.00345262,0.00320583,0.00297623,0.00276281,0.00256456,0.00238048,0.00220971,0.00205132,0.00190449,0.00176847,0.00164236,0.00152535,0.00141672,0.00131595,0.00122239,0.00113555,0.00105494,0.00098014,0.00091066,0.00084619,0.00078629,0.00073068,0.00067899,0.00063101,0.00058644,0.00054511,0.00050672,0.00047111,0.00043805,0.00040741,0.000378962,0.000352543,0.000328001,0.000305208,0.000284041,0.000264375,0.000246109,0.000229143,0.000213376,0.00019873,0.000185115,0.000172454,0.000160678,0.00014973,0.00013955,0.000130086,0.00012129,0.000113106,0.000105501,0.000098428,0.000091853,0.000085738,0.000080048,0.000074751,0.000069819,0.000065222,0.000060939,0.000056942,0.000053217,0.000049737,0.000046491,0.000043464,0.000040635,0.000038,0.00003554,0.000033245,0.000031101,0.000029099,0.000027231,0.000025486,0.000023856,0.000022333,0.00002091,0.000019581,0.000018338,0.000017178,0.000016093,0.00001508,0.000014134,0.000013249,0.000012423,0.00001165,0.000010928,0.000010252,0.00000962,0.000009028,0.000008474,0.000007955,0.000007469,0.000007013,0.000006586,0.000006186,0.000005811,0.000005459,0.00000513,0.000004821,0.000004531,0.000004259,0.000004004,0.000003765,0.00000354,0.000003329,0.000003131,0.000002945,0.000002771,0.000002607,0.000002453,0.000002309,0.000002173,0.000002046,0.000001927,0.000001814,0.000001709,0.00000161,0.000001517,0.000001429,0.000001347,0.000001269,0.000001197,0.000001128,0.000001064,0.000001003,0.000000946,0.000000893,0.000000842,0.000000795,0.00000075,0.000000707,0.000000667,0.00000063
        ],
        Z: [
            0.000000535,0.000000811,0.000001221,0.000001829,0.000002722,0.000004028,0.000005926,0.000008665,0.000012596,0.000018201,0.000026144,0.00003733,0.000052987,0.000074764,0.00010487,0.00014622,0.00020266,0.00027923,0.00038245,0.00052072,0.000704776,0.00094823,0.0012682,0.0016861,0.0022285,0.0029278,0.0038237,0.0049642,0.0064067,0.0082193,0.0104822,0.013289,0.016747,0.02098,0.026127,0.032344,0.039802,0.048691,0.05921,0.071576,0.0860109,0.10274,0.122,0.14402,0.16899,0.19712,0.22857,0.26347,0.3019,0.34387,0.389366,0.43797,0.48922,0.5429,0.59881,0.65676,0.71658,0.77812,0.84131,0.90611,0.972542,1.039,1.103,1.165,1.225,1.282,1.338,1.393,1.446,1.499,1.553,1.607,1.659,1.708,1.755,1.798,1.839,1.877,1.91,1.941,1.967,1.989,2.006,2.017,2.024,2.027,2.026,2.022,2.015,2.006,1.995,1.981,1.965,1.946,1.925,1.901,1.874,1.845,1.814,1.781,1.745,1.709,1.672,1.635,1.596,1.555,1.512,1.467,1.42,1.37,1.318,1.262,1.205,1.147,1.088,1.03,0.97383,0.91943,0.86746,0.81828,0.772125,0.72829,0.68604,0.64553,0.60685,0.57006,0.53522,0.50234,0.4714,0.44239,0.415254,0.390024,0.366399,0.344015,0.322689,0.302356,0.283036,0.264816,0.247848,0.232318,0.218502,0.205851,0.193596,0.181736,0.170281,0.159249,0.148673,0.138609,0.129096,0.120215,0.112044,0.10471,0.098196,0.092361,0.087088,0.082248,0.077744,0.073456,0.069268,0.06506,0.060709,0.056457,0.052609,0.049122,0.045954,0.04305,0.040368,0.037839,0.035384,0.032949,0.030451,0.028029,0.025862,0.02392,0.022174,0.020584,0.019127,0.01774,0.016403,0.015064,0.013676,0.012308,0.011056,0.009915,0.008872,0.007918,0.00703,0.006223,0.005453,0.004714,0.003988,0.003289,0.002646,0.002063,0.001533,0.001091,0.000711,0.000407,0.000184,0.000047,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
        ]
    }
];


/**
 * @typedef {object} _SpectralData
 * @property {number}   startnm  First wavelength in `data`, in nm.
 * @property {number}   endnm    Last  wavelength in `data`, in nm.
 * @property {number}   step     Spacing between consecutive `data` values, in nm.
 * @property {number[]} data     Reflectance / transmittance / SPD samples.
 *                               For reflectance/transmittance these are typically
 *                               0.0 - 1.0 (or 0 - 100 if you stay consistent —
 *                               the k normaliser cancels the unit out).
 */

/**
 * Spectral data wrangler and reflectance → XYZ integrator.
 *
 * See the file-top primer for what spectral data is, what the bundled
 * illuminants/observers represent, and the math that calculateXYZ() runs.
 *
 * Stateless — instances are cheap, you can keep one around for the lifetime
 * of the app or new one per call. The Illuminants and Observers tables are
 * module-level and shared.
 *
 * @example
 *   var s = new Spectral();
 *   var spectrum = s.toSpectral(380, 730, reflArr, 10);
 *   var xyz = s.calculateXYZ(spectrum, s.getIlluminant('D50'), s.getObserver('2'));
 */
class Spectral {

    constructor() {
        this.version = '0.0.1';
        this.name = 'Spectral';
        this.description = 'Spectral data and calculations';
    }

    /**
     * @returns {object[]} The full Illuminants[] table — useful for building
     *                     a UI dropdown of available light sources. Treat as
     *                     read-only (callers share the same array reference).
     */
    getIlluminants = function () {
        return Illuminants;
    };

    /**
     * Look up an illuminant by short name.
     * @param {string} name  'A' | 'C' | 'D50' | 'D55' | 'D65'.
     *                       Case-sensitive — names are uppercase.
     * @returns {object|false} The illuminant entry, or false if not found.
     *                         To add F-series / LED illuminants, extend the
     *                         module-level Illuminants[] array using the
     *                         schema documented above the array.
     */
    getIlluminant = function (name) {
        for (var i = 0; i < Illuminants.length; i++) {
            if (name === Illuminants[i].name) {
                return Illuminants[i];
            }
        }
        return false;
    };

    /**
     * @returns {object[]} The full Observers[] table — useful for building
     *                     a UI dropdown of "2°" vs "10°". Treat as read-only.
     */
    getObservers = function () {
        return Observers;
    };

    /**
     * Look up an observer by short name.
     * @param {string} name  '2'  (CIE 1931, 2°) or
     *                       '10' (CIE 1964, 10°).
     * @returns {object|false} The observer entry, or false if not found.
     */
    getObserver = function (name) {
        for (var i = 0; i < Observers.length; i++) {
            if (name === Observers[i].name) {
                return Observers[i];
            }
        }
        return false;
    };

    /**
     * Wrap a raw reflectance / transmittance / SPD array in the shape that
     * calculateXYZ() expects.
     *
     * If `nmStep` is omitted it is computed from the start/end and array
     * length — but see the TODO below; pass it explicitly to be safe.
     *
     * Use this for spectrophotometer output. Common spectro grids:
     *   380 - 730 nm @ 10 nm  (36 values)  — i1 Pro classic / many older instruments
     *   380 - 780 nm @ 10 nm  (41 values)  — i1 Pro 2 / 3
     *   380 - 730 nm @  5 nm  (71 values)  — high-resolution mode
     *   400 - 700 nm @ 10 nm  (31 values)  — ASTM E308 truncated range
     *
     * The `data` units don't matter (reflectance can be 0-1 or 0-100) — the
     * k normaliser inside calculateXYZ scales the result so that a perfect
     * diffuser (R(λ) = 1 everywhere) returns Y = 100 under any illuminant.
     *
     * TODO (bug): nmStep auto-derivation has a sign error — the formula
     * should be `(endnm - startnm) / (data.length - 1)`, not the reverse.
     * As written it returns a negative step. Workaround: always pass
     * `nmStep` explicitly. Fix when next touching the file.
     *
     * @param {number}   startnm  First wavelength sample, in nm.
     * @param {number}   endnm    Last  wavelength sample, in nm.
     * @param {number[]} data     Sample values at startnm, startnm+step, ...
     * @param {number}  [nmStep]  Spacing in nm. Recommended.
     * @returns {_SpectralData}
     */
    toSpectral = function (startnm, endnm, data, nmStep) {
        if (!nmStep) {
            nmStep = (startnm - endnm) / (data.length - 1);
        }
        return {
            startnm: startnm,
            endnm: endnm,
            step: nmStep,
            data: data
        }
    };

    /**
     * Integrate a spectrum against an illuminant SPD and an observer's
     * colour-matching functions to produce CIE XYZ tristimulus values.
     *
     * This is the heart of the module. It implements the standard CIE
     * tristimulus integration:
     *
     *      X = k · Σ S(λ) · R(λ) · x̄(λ)
     *      Y = k · Σ S(λ) · R(λ) · ȳ(λ)
     *      Z = k · Σ S(λ) · R(λ) · z̄(λ)
     *      k = 100 / Σ S(λ) · ȳ(λ)
     *
     * The integration is driven by `spectrum`'s wavelength grid. For each
     * sample wavelength, the illuminant and observer are linearly
     * interpolated when they don't land exactly on their own grids — so it
     * is fine to mix a 10-nm spectrum with a 1-nm observer or a 5-nm
     * illuminant. Out-of-range wavelengths are clamped to whichever input
     * has the narrower coverage (so e.g. integrating against Illuminant C,
     * which only covers 380-780 nm, won't reach into 300 nm UV even if your
     * spectrum does).
     *
     * The returned XYZ object inherits the illuminant's whitePoint, so:
     *
     *      var xyz = spectral.calculateXYZ(spectrum, D50, obs2);
     *      var lab = convert.XYZ2Lab(xyz);   // Lab values measured under D50
     *
     *      var xyzD65 = spectral.calculateXYZ(spectrum, D65, obs2);
     *      var labD65 = convert.XYZ2Lab(xyzD65);
     *
     * Calling with two different illuminants and comparing the resulting Lab
     * pairs is the basis of metamerism / illuminant-mismatch checks.
     *
     * Performance: this is the accuracy path — designed to be called once
     * per measurement, not per pixel. A profile build with a TC1617 chart
     * runs ~1617 calculateXYZ() per illuminant per intent, which is plenty
     * fast. If you need per-pixel spectral rendering, build a LUT.
     *
     * @param {_SpectralData} spectrum   Reflectance / transmittance spectrum
     *                                   from a spectro or library.
     * @param {object}        illuminant Entry from getIlluminant() / Illuminants[].
     * @param {object}        observer   Entry from getObserver()   / Observers[].
     * @returns {_cmsXYZ} XYZ object {type, X, Y, Z, whitePoint} where Y is
     *                   normalised so a perfect diffuser yields Y = 100.
     *                   The whitePoint matches `illuminant.whitePoint` so
     *                   downstream Lab conversion is illuminant-correct.
     */
    calculateXYZ = function (spectrum, illuminant, observer) {

        // calculate based on spectrum
        var spectralStart = spectrum.startnm;
        var spectralEnd = spectrum.endnm;
        var sIndexStart, sIndexEnd, sCount, index, frac;
        var sumX = 0, sumY = 0, sumZ = 0, sumK = 0;
        var sy, Xk, Yk, Zk, k, X, Y, Z;
        var oX, oY, oZ, ilum;

        // Check ranges
        if (spectralStart < illuminant.startnm) {
            spectralStart = illuminant.startnm;
        }

        if (spectralStart < observer.startnm) {
            spectralStart = observer.startnm;
        }

        if (spectralEnd > illuminant.endnm) {
            spectralEnd = illuminant.endnm
        }

        if (spectralEnd > observer.endnm) {
            spectralEnd = observer.endnm
        }

        sCount = (spectralEnd - spectralStart) / spectrum.step;
        sIndexStart = (spectralStart - spectrum.startnm) / spectrum.step;
        sIndexEnd = sIndexStart + sCount;

        var wavelength = spectralStart;
        for (var i = sIndexStart; i <= sIndexEnd; i++) {

            // calc observer index
            var oi = (wavelength - observer.startnm) / observer.step;
            if (oi % 1 !== 0) {
                // interpolate
                index = Math.floor(oi);
                frac = oi - index;
                oX = (observer.X[index] * (1 - frac)) + (observer.X[index + 1] * frac);
                oY = (observer.Y[index] * (1 - frac)) + (observer.Y[index + 1] * frac);
                oZ = (observer.Z[index] * (1 - frac)) + (observer.Z[index + 1] * frac);
            } else {
                oX = observer.X[oi];
                oY = observer.Y[oi];
                oZ = observer.Z[oi];
            }

            // calc illuminant data index
            var ii = (wavelength - illuminant.startnm) / illuminant.step;
            if (ii % 1 !== 0) {
                // interpolate
                index = Math.floor(ii);
                frac = ii - index;
                ilum = (illuminant.data[index] * (1 - frac)) + (illuminant.data[index + 1] * frac);
            } else {
                ilum = illuminant.data[ii];
            }

            sy = ilum * oY;

            Xk = oX * ilum * spectrum.data[i];
            Yk = oY * ilum * spectrum.data[i];
            Zk = oZ * ilum * spectrum.data[i];

            sumX += Xk;
            sumY += Yk;
            sumZ += Zk;
            sumK += sy;
            wavelength += spectrum.step;
        }

        k = 100 / sumK; // normalise range 0.0 - 1.0

        X = sumX * k / 100; // Normalizing Constant
        Y = sumY * k / 100;
        Z = sumZ * k / 100;

        // var chromaticity = {x:0, y:0,z:0};
        // if(x + y + z !== 0){
        //     chromaticity.x = x / (x + y + z);
        //     chromaticity.y = y / (x + y + z);
        //     chromaticity.z = z / (x + y + z);
        // }

        return convert.XYZ(X, Y, Z, illuminant.whitePoint);
    }

}

module.exports = Spectral;