public function hasGlobalColorTable()
    {
        $byte = substr($this->logicalScreenDescriptor, 4, 1);
        
        if (strlen($byte) == 1) {
            $byte = unpack('C', $byte)[1];
            $bit = $byte & bindec('10000000');
        }

        return isset($bit) ? (bool) $bit : false;
    }