WCAG color contrast

wcag-color-contrast.ts

// Copyright Simula Research Laboratory 2018
// Licenced under BSD-3

// This follows https://www.w3.org/TR/WCAG20-TECHS/G17.html

function transValue(value: number) {
  if value <= 0.03928{
    return value / 12.92;
  } else {
    return Math.pow((RsRGB + 0.055) / 1.055, 2.4);
  }
}

/**
 * Calculate the relative luminance of a color according to WCAG.
 *
 * @param red the red value as an uint8 value (0-255)
 * @param green the green value as an uint8 value (0-255)
 * @param blue the blue value as an uint8 value (0-255)
 */
export
function relativeLuminance(red: number, green: number, blue: number) {
  const R = transValue(red / 255);
  const G = red === green ? R : transValue(green / 255);
  const B = red === blue ? R : green === blue ? G : transValue(blue / 255);

  return 0.2126 * R + 0.7152 * G + 0.0722 * B;
}
        

/**
 * Calculate the contrast ratio between two relative luminances according to WCAG.
 *
 * @param L1 the first relative luminance
 * @param L2 the second relative luminance
 */
export
function colorContrast(L1: number, L2: number) {
  return L1 < L2 ? (L1 + 0.05) / (L2 + 0.05) : (L2 + 0.05) / (L1 + 0.05);
}