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"use strict";
Object.defineProperty(exports, "__esModule", {
value: true
});
exports.blendWithWhite = blendWithWhite;
exports.colorDeltaE94 = colorDeltaE94;
exports.rgb2gray = rgb2gray;
exports.srgb2xyz = srgb2xyz;
exports.xyz2lab = xyz2lab;
/**
* Copyright (c) Microsoft Corporation.
*
* Licensed under the Apache License, Version 2.0 (the 'License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
function blendWithWhite(c, a) {
return 255 + (c - 255) * a;
}
function rgb2gray(r, g, b) {
// NOTE: this is the exact integer formula from SSIM.js.
// See https://github.com/obartra/ssim/blob/ca8e3c6a6ff5f4f2e232239e0c3d91806f3c97d5/src/matlab/rgb2gray.ts#L56
return 77 * r + 150 * g + 29 * b + 128 >> 8;
}
// Percieved color difference defined by CIE94.
// See https://en.wikipedia.org/wiki/Color_difference#CIE94
//
// The result of 1.0 is a "just-noticiable difference".
//
// Other results interpretation (taken from http://zschuessler.github.io/DeltaE/learn/):
// < 1.0 Not perceptible by human eyes.
// 1-2 Perceptible through close observation.
// 2-10 Perceptible at a glance.
// 11-49 Colors are more similar than opposite
// 100 Colors are exact opposite
function colorDeltaE94(rgb1, rgb2) {
const [l1, a1, b1] = xyz2lab(srgb2xyz(rgb1));
const [l2, a2, b2] = xyz2lab(srgb2xyz(rgb2));
const deltaL = l1 - l2;
const deltaA = a1 - a2;
const deltaB = b1 - b2;
const c1 = Math.sqrt(a1 ** 2 + b1 ** 2);
const c2 = Math.sqrt(a2 ** 2 + b2 ** 2);
const deltaC = c1 - c2;
let deltaH = deltaA ** 2 + deltaB ** 2 - deltaC ** 2;
deltaH = deltaH < 0 ? 0 : Math.sqrt(deltaH);
// The k1, k2, kL, kC, kH values for "graphic arts" applications.
// See https://en.wikipedia.org/wiki/Color_difference#CIE94
const k1 = 0.045;
const k2 = 0.015;
const kL = 1;
const kC = 1;
const kH = 1;
const sC = 1.0 + k1 * c1;
const sH = 1.0 + k2 * c1;
const sL = 1;
return Math.sqrt((deltaL / sL / kL) ** 2 + (deltaC / sC / kC) ** 2 + (deltaH / sH / kH) ** 2);
}
// sRGB -> 1-normalized XYZ (i.e. Y ∈ [0, 1]) with D65 illuminant
// See https://en.wikipedia.org/wiki/SRGB#From_sRGB_to_CIE_XYZ
function srgb2xyz(rgb) {
let r = rgb[0] / 255;
let g = rgb[1] / 255;
let b = rgb[2] / 255;
r = r > 0.04045 ? Math.pow((r + 0.055) / 1.055, 2.4) : r / 12.92;
g = g > 0.04045 ? Math.pow((g + 0.055) / 1.055, 2.4) : g / 12.92;
b = b > 0.04045 ? Math.pow((b + 0.055) / 1.055, 2.4) : b / 12.92;
return [r * 0.4124 + g * 0.3576 + b * 0.1805, r * 0.2126 + g * 0.7152 + b * 0.0722, r * 0.0193 + g * 0.1192 + b * 0.9505];
}
const sigma_pow2 = 6 * 6 / 29 / 29;
const sigma_pow3 = 6 * 6 * 6 / 29 / 29 / 29;
// 1-normalized CIE XYZ with D65 to L*a*b*
// See https://en.wikipedia.org/wiki/CIELAB_color_space#From_CIEXYZ_to_CIELAB
function xyz2lab(xyz) {
const x = xyz[0] / 0.950489;
const y = xyz[1];
const z = xyz[2] / 1.088840;
const fx = x > sigma_pow3 ? x ** (1 / 3) : x / 3 / sigma_pow2 + 4 / 29;
const fy = y > sigma_pow3 ? y ** (1 / 3) : y / 3 / sigma_pow2 + 4 / 29;
const fz = z > sigma_pow3 ? z ** (1 / 3) : z / 3 / sigma_pow2 + 4 / 29;
const l = 116 * fy - 16;
const a = 500 * (fx - fy);
const b = 200 * (fy - fz);
return [l, a, b];
}