resize ing image whn uploading php

I have a requirment to reseize a image whn uploding, it is working fine, but if i upload big image. it is resizing the images, pleae can u all help.


here is my code

<?
include '../../db/cnn.php';

$sSqlSel="SELECT max(id) sid FROM testimage";
$sSqsel=mysql_query($sSqlSel);
$nRec=mysql_num_rows($sSqsel);
$sDatawis=mysql_fetch_object($sSqsel);
$sIds=$sDatawis->sid;
$sIncId=$sIds+(int)2;

$sDispThFull="/webgate/cms/admin/images/full/";
$sDispThThum="/webgate/cms/admin/images/thum/";

if($_POST['Submit']) {

if($_FILES['photo1']['tmp_name']){
$sRoot=$_SERVER['DOCUMENT_ROOT'];
$uploadDir = $sRoot .'/webgate/cms/admin/images/full/';
$uploadDir1= $sRoot .'/webgate/cms/admin/images/thum/';

$sFile =$_FILES['photo1']['name'];
$sPath=$_FILES['photo1']['tmp_name'];

$sExt=strrev(substr(strrev($sFile),0,strpos(strrev($sFile),".")));
//$sExt=substr($sFile,(strlen($sFile)-3),3);
$sFilePath ="img" . $sIncId . "." . $sExt; //
$sPhoto1=$sFilePath;

$uploadFile = $uploadDir . $sFilePath;

move_uploaded_file($sPath,$uploadFile); //

$n_width=100; // Fix the width of the thumb nail images
$n_height=100; // Fix the height of the thumb nail imaage
$uploadFile1 = $uploadDir1 . $sFilePath;

if($sExt=="jpg"){
$im=ImageCreateFromJPEG($uploadFile);
$width=ImageSx($im); // Original picture width is stored
$height=ImageSy($im); // Original picture height is stored
$newimage=imagecreatetruecolor($n_width,$n_height);
imageCopyResized($newimage,$im,0,0,0,0,$n_width,$n_height,$width,$height);
ImageJpeg($newimage,$uploadFile1);
chmod("$uploadFile1",0777);
}

if($sExt=="gif"){
$im=ImageCreateFromGIF($uploadFile);
$width=ImageSx($im); // Original picture width is stored
$height=ImageSy($im); // Original picture height is stored
$newimage=imagecreatetruecolor($n_width,$n_height);
imageCopyResized($newimage,$im,0,0,0,0,$n_width,$n_height,$width,$height);
ImageGIF($newimage,$uploadFile1);
chmod("$uploadFile1",0777);
}

if($sExt=="png"){
$im=ImageCreateFromPNG($uploadFile);
$width=ImageSx($im); // Original picture width is stored
$height=ImageSy($im); // Original picture height is stored
$newimage=imagecreatetruecolor($n_width,$n_height);
imageCopyResized($newimage,$im,0,0,0,0,$n_width,$n_height,$width,$height);
ImagePNG($newimage,$uploadFile1);
chmod("$uploadFile1",0777);
}
}
$sSql="INSERT INTO testimage(imgsrc) VALUES('$sPhoto1')";
$select=mysql_query($sSql);

if($select){
print "ok";
} else {
print "no" . mysql_error();
}
}
?>