gdlib problem

Jeg bruger følgende kode:

<html>
    <head>
        <title>
        Statistik
        </title>
    </head>
    <body>

<?

$stat1 = 25;
$stat2 = 25;
$stat3 = 50;

$gif = ImageCreate(117,55);
$bg = ImageColorAllocate($gif,255,255,255);
$ram1 = ImageColorAllocate($gif,50,115,75);
$ram2 = ImageColorAllocate($gif,50,115,75);
$ram3 = ImageColorAllocate($gif,50,115,75);
$tx1 = ImageColorAllocate($gif,0,0,0);
$tx2 = ImageColorAllocate($gif,0,0,0);
$tx3 = ImageColorAllocate($gif,0,0,0);
ImageFilledRectangle($gif,0,0,100,100,$bg1);
ImageFilledRectangle($gif,15,5,($stat1 + 15),7,$ram1);
ImageFilledRectangle($gif,15,25,($stat2 + 15),27,$ram2);
ImageFilledRectangle($gif,15,45,($stat3 + 15),47,$ram3);
ImageString($gif,2,0,0,$stat1,$tx1);
ImageString($gif,2,0,20,$stat2,$tx1);
ImageString($gif,2,0,40,$stat3,$tx1);
header("content-type: image/png");
ImagePNG($gif);
?>

   
    </body>
</html>

Har fundet det har på eksperten. Men mit output biver således:

Warning: Cannot modify header information - headers already sent by (output started at c:\inetpub\wwwroot\webtermometer\www\default.php:9) in c:\inetpub\wwwroot\webtermometer\www\default.php on line 30
‰PNG  IHDRu7ÀºèPLTEÿÿÿ2sK2sK2sKYßã‚€IDATxœí”Á €@ £¦í@lÁö‘þk2î£ëã3ç°ù jbÎ…€4Ã6–Š¹UÕMºˆ¡\½|ĺ8×ägJ’¤s_[ÅÚªž}Źˆ¡Üì«$éK)+®{ªtnüï´ßñ˜ Ú•÷.…‹ô®JY‘±ãá˜(¶¶'IEND®B`‚

Nogen der kan fortælle mig hvorfor?