image text centered

imagetext.php

<?

header('Content-Type: image/png');
	$size= 80;
		$extImg = imagecreatetruecolor($size,$size);

$targetFileImg = 'mime.png';
$ext = trim($_GET['t']);

		$ctext = imagecolorallocate($extImg, 100, 100, 100);  //testo
		$ctrasp = imagecolorallocate($extImg, 200,200,200);  //sfondo

	  	imagefilledrectangle($extImg,0,0,$size,$size,$ctrasp);

		$font = 5;#imageloadfont('trebuc.ttf');
		$fontW = ImageFontWidth($font);
		$fontH = ImageFontHeight($font);
		
		$textW = $fontW * strlen($ext);
		$textCenter = ceil(($size - $textW) / 2);
		$textH = $fontH;
		$textMiddle = ceil(($size - $textH) / 2);

		imagestring($extImg, $font, $textCenter, $textMiddle, $ext, $ctext);
		
		imagepng($extImg);//crea file thumb!
		imagedestroy($extImg);

?>