itowns/lib/Renderer/Color.js

A JS/WebGL framework for 3D geospatial data visualization

export function lab2rgb(lab) {
  let y = (lab[0] + 16) / 116;
  let x = lab[1] / 500 + y;
  let z = y - lab[2] / 200;
  let r;
  let g;
  let b;
  x = 0.95047 * (x * x * x > 0.008856 ? x * x * x : (x - 16 / 116) / 7.787);
  y = 1.00000 * (y * y * y > 0.008856 ? y * y * y : (y - 16 / 116) / 7.787);
  z = 1.08883 * (z * z * z > 0.008856 ? z * z * z : (z - 16 / 116) / 7.787);
  r = x * 3.2406 + y * -1.5372 + z * -0.4986;
  g = x * -0.9689 + y * 1.8758 + z * 0.0415;
  b = x * 0.0557 + y * -0.2040 + z * 1.0570;
  r = r > 0.0031308 ? 1.055 * r ** (1 / 2.4) - 0.055 : 12.92 * r;
  g = g > 0.0031308 ? 1.055 * g ** (1 / 2.4) - 0.055 : 12.92 * g;
  b = b > 0.0031308 ? 1.055 * b ** (1 / 2.4) - 0.055 : 12.92 * b;
  return [Math.max(0, Math.min(1, r)) * 255, Math.max(0, Math.min(1, g)) * 255, Math.max(0, Math.min(1, b)) * 255];
}
export function rgb2lab(rgb) {
  let r = rgb.r || rgb[0] / 255;
  let g = rgb.g || rgb[1] / 255;
  let b = rgb.b || rgb[2] / 255;
  let x;
  let y;
  let z;
  r = r > 0.04045 ? ((r + 0.055) / 1.055) ** 2.4 : r / 12.92;
  g = g > 0.04045 ? ((g + 0.055) / 1.055) ** 2.4 : g / 12.92;
  b = b > 0.04045 ? ((b + 0.055) / 1.055) ** 2.4 : b / 12.92;
  x = (r * 0.4124 + g * 0.3576 + b * 0.1805) / 0.95047;
  y = (r * 0.2126 + g * 0.7152 + b * 0.0722) / 1.00000;
  z = (r * 0.0193 + g * 0.1192 + b * 0.9505) / 1.08883;
  x = x > 0.008856 ? x ** (1 / 3) : 7.787 * x + 16 / 116;
  y = y > 0.008856 ? y ** (1 / 3) : 7.787 * y + 16 / 116;
  z = z > 0.008856 ? z ** (1 / 3) : 7.787 * z + 16 / 116;
  return [116 * y - 16, 500 * (x - y), 200 * (y - z)];
}

// calculate the perceptual distance between colors in CIELAB
// https://github.com/THEjoezack/ColorMine/blob/master/ColorMine/ColorSpaces/Comparisons/Cie94Comparison.cs
export function deltaE(rgbA, rgbB) {
  const labA = rgb2lab(rgbA);
  const labB = rgb2lab(rgbB);
  const deltaL = labA[0] - labB[0];
  const deltaA = labA[1] - labB[1];
  const deltaB = labA[2] - labB[2];
  const c1 = Math.sqrt(labA[1] * labA[1] + labA[2] * labA[2]);
  const c2 = Math.sqrt(labB[1] * labB[1] + labB[2] * labB[2]);
  const deltaC = c1 - c2;
  let deltaH = deltaA * deltaA + deltaB * deltaB - deltaC * deltaC;
  deltaH = deltaH < 0 ? 0 : Math.sqrt(deltaH);
  const deltaLKlsl = deltaL / 1.0;
  const deltaCkcsc = deltaC / (1.0 + 0.045 * c1);
  const deltaHkhsh = deltaH / (1.0 + 0.015 * c1);
  const i = deltaLKlsl * deltaLKlsl + deltaCkcsc * deltaCkcsc + deltaHkhsh * deltaHkhsh;
  return i < 0 ? 0 : Math.sqrt(i);
}