hi all i need some help with what im working on

i want to put some text in the middle of a picture and make the picture transparent by about 50%

i would like the text to be about 24 in size and bold

i have got this to now

Code:
$iOut = imagecreatetruecolor ("1268","202") ; 
$text_color = imagecolorallocate($iOut, 233, 14, 91);
imagestring($iOut, 1000, 500, 100,  'A Simple Text String monkey', $text_color);
imagepng($iOut,$_SERVER["DOCUMENT_ROOT"].'/php/videos/hide/header2.jpg');
imagedestroy($iOut);