problem s imagecreatefrompng

<?php
session_start();
include "funkce.php";
$id=$_SESSION["id"];
   $result = 0;
   $cas=StrFTime("%H-%M-%S", Time());
   $datum=StrFTime("%Y-%m-%d");
   $jmeno=$_FILES['myfile']['name'];
   $nazev=$datum."-".$cas."-".$jmeno;
   $target_path = "avatari/".$nazev;

   if(@move_uploaded_file($_FILES['myfile']['tmp_name'], $target_path)) 
   {
      $result = 1;
      $vysledek=mysql_query("UPDATE uzivatele SET avatar='$nazev' WHERE id='$id' ");
      $obrazek = GetImageSize($target_path);
      $sirka = $obrazek[0];
      $vyska = $obrazek[1];
      $typ = $obrazek[2];
      if ($sirka > 100 || $vyska > 00) 
      {
      $pomer = max($sirka,$vyska)/100;
      $thumb_sirka = round($sirka/$pomer);
      $thumb_vyska = round($vyska/$pomer);      
      }
      $thumb = imagecreatetruecolor($thumb_sirka, $thumb_vyska);
      if($typ==2)
      {
        $source = imagecreatefromjpeg($target_path);
        imageinterlace($thumb, 1);
        
        // ZMENIM VELIKSOT
        imagecopyresized($thumb, $source, 0, 0, 0, 0, $thumb_sirka, $thumb_vyska,
        $sirka, $vyska);
  
        // VÝSTUP
        imagejpeg($thumb, $target_path, 90);
      }
      if($typ==1)
      {
        $source = imagecreatefromgif($target_path);
        imageinterlace($thumb, 1);
        
        // ZMENIM VELIKSOT
        imagecopyresized($thumb, $source, 0, 0, 0, 0, $thumb_sirka, $thumb_vyska,
        $sirka, $vyska);
  
        // VÝSTUP
        imagegif($thumb, $target_path, 90);
      }
      if($typ==3)
      {
        $source = imagecreatefrompng($target_path);
        imageinterlace($thumb, 1);
        
        // ZMENIM VELIKSOT
        imagecopyresized($thumb, $source, 0, 0, 0, 0, $thumb_sirka, $thumb_vyska,
        $sirka, $vyska);
  
        // VÝSTUP
        imagepng($thumb, $target_path, 90);
      }
   }
   
   
   sleep(1);
?>

<script language="javascript" type="text/javascript">window.top.window.stopUpload(<?php echo $result; ?>);</script>