How do you get a GDImage from a chillerlan qtcode

Question

I use chillerlan qr_code to generate a qrcode in php.

$gdImage = (new QRCode ($options)) ->render('https://www.youtube.com/');

I can echo the qrcode on the screen as a qrcode. I can also printit as a string. BUT the following call returns false.

$gdImage2 =@imagecreatefromstring($gdImage);

How can I create a GDImage of my qr Code?

Thanks,