PHP - save imagettftext created as a image?

Hi,
I have used the PHP script below to create and display a text image which works fine, but how do I then save this as actual image in my images folder and call it say “menu_button_12.png”

Thanks in advance for your feedback.

<?php
// Set the content-type
header('Content-Type: image/png');

// Create the image
$im = imagecreatetruecolor(200, 30);

// Create some colors
$white = imagecolorallocate($im, 255, 255, 255);
$grey = imagecolorallocate($im, 128, 128, 128);
$blue = imagecolorallocate($im, 40, 77, 146);
$black = imagecolorallocate($im, 0, 0, 0);
imagefilledrectangle($im, 0, 0, 200, 30, $blue);

// The text to draw
$text = 'News and Events';

$rootd = $_SERVER['DOCUMENT_ROOT']."/";
 
// Replace path by your own font path
$font = $root.'bisa_alternates.ttf';

// Add some shadow to the text
imagettftext($im, 24, 0, 11, 25, $grey, $font, $text);

// Add the text
imagettftext($im, 24, 0, 10, 24, $white, $font, $text);

// Using imagepng() results in clearer text compared with imagejpeg()
imagepng($im);
imagedestroy($im);
?>