@libgranite/contrast-color/index.js

Contrast color calculator

/**
 * Granite Framework Contrast Color
 *
 * This package calculates the best color (white or black) to have the highest
 * contrast against a specified color.
 */

function hex_to_rgb(color_hex) {
  var buffer = new ArrayBuffer(4);
  var data_view = new DataView(buffer);
  data_view.setUint32(0,parseInt(color_hex, 16),false);
  var color_bytes = new Uint8Array(buffer);

  return {
    red: color_bytes[0],
    green: color_bytes[1],
    blue: color_bytes[2]
  };
}

function rgb_to_hex(red, green, blue) {
  return "#" + (1 << 24 | red << 16 | green << 8 | blue).toString(16).slice(1);
}

export function get_contrast_color_rgb(color) {
  var red = color.red;
  red = red * red * .299;

  var green = color.green;
  green = green * green * .587;
  
  var blue = color.blue;
  blue = blue * blue * .114;
  
  var luminance = red + blue + green;
  if (luminance > 16900) {
    return 'black';
  }
  else {
    return 'white';
  }
}

export function get_contrast_color_hex(color) {
  var rgb_color = hex_to_rgb(color);
  return get_contrast_color_rgb(rgb_color);
}