[PHP] Get the brightness of a color

get_brightness.php

<?php
/**
 * Get the brightness of the color.
 * The return value is between 0 and 1.
 * 0 = light
 * 1 = dark
 * 
 * @param string $hex The hex code of the color
 * @return float|int
 */
function get_brightness($hex) {
    $hex = str_replace('#', '', $hex);

    $c_r = hexdec(substr($hex, 0, 2));
    $c_g = hexdec(substr($hex, 2, 2));
    $c_b = hexdec(substr($hex, 4, 2));

    return (($c_r * 299) + ($c_g * 587) + ($c_b * 114)) / 1000 / 255;
}