Funktionen imagepng virker ikke

Hey alle.

Bruger dette script på en af mine sider:

<?php
        if(isset($_POST['submit'])){
          if (isset ($_FILES['new_image'])){
              $imagename = $_FILES['new_image']['name'];
              $source = $_FILES['new_image']['tmp_name'];
              $target = "images/".$imagename;
              move_uploaded_file($source, $target);
 
              $imagepath = $imagename;
              $save = "images/" . $imagepath; //This is the new file you saving
              $file = "images/" . $imagepath; //This is the original file
 
              list($width, $height) = getimagesize($file) ; 
 
              $modwidth = 150; 
 
              $diff = $width / $modwidth;
 
              $modheight = $height / $diff; 
              $tn = imagecreatetruecolor($modwidth, $modheight) ; 
              $image = imagecreatefromjpeg($file) ; 
              imagecopyresampled($tn, $image, 0, 0, 0, 0, $modwidth, $modheight, $width, $height) ; 
 
              imagejpeg($tn, $save, 100) ; 
 
              $save = "images/sml_" . $imagepath; //This is the new file you saving
              $file = "images/" . $imagepath; //This is the original file
 
              list($width, $height) = getimagesize($file) ; 
 
              $modwidth = 80; 
 
              $diff = $width / $modwidth;
 
              $modheight = $height / $diff; 
              $tn = imagecreatetruecolor($modwidth, $modheight) ; 
              $image = imagecreatefromjpeg($file) ; 
              imagecopyresampled($tn, $image, 0, 0, 0, 0, $modwidth, $modheight, $width, $height) ; 
 
              imagejpeg($tn, $save, 100) ; 
            echo "Large image: <img src='images/".$imagepath."'><br>"; 
            echo "Thumbnail: <img src='images/sml_".$imagepath."'>"; 
 
          }
        }
?

Som er fundet her inde: http://www.theopensurgery.com/29/php-upload-and-resize-image-script/

Jeg har prøvet at lave så den virker på png billeder, ved at lave imagecreatefromjpeg om til imagecreatefrompng og imagejpeg om til imagepng, men det virker stadig ikke.

Nogle foreslag?