Find the brightness of HEX color

function get_brightness($hex) {
// returns brightness value from 0 to 255

// strip off any leading #
$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;
}

It will return the brightness.
if ($this->get_brightness($msg_color) > 130){$text_color='black';}
                    else {$text_color='white';}