php生成缩略图的效能

php生成缩略图的功能
客户自己上传的图片大小不标准，想让传上来的图片统一变成150X113尺寸的。从网上搜到的程序在IE里用正常，到了别的浏览器（如搜狗浏览器等）就不行，这是什么原因？（感觉老是不执行）
代码如下：

<?php
session_start();
if (isset($_SESSION['adminname']) && isset($_SESSION['adminpass'])){

//****************************************
//生成缩略图========================================
$myname=date("YmdHis");

$filename="product/min/".$myname; //小图片文件名
$resizewidth=150; // 生成图片的宽度
$resizeheight=113; // 生成图片的高度

function ResizeImage($im,$maxwidth,$maxheight,$name){
$resizewidth = $resizeheight = false;

$width = imagesx($im);
$height = imagesy($im);
if(($maxwidth && $width > $maxwidth) || ($maxheight && $height > $maxheight)){
if($maxwidth && $width > $maxwidth){
$widthratio = $maxwidth/$width;
$resizewidth=true;
}
if($maxheight && $height > $maxheight){
$heightratio = $maxheight/$height;
$resizeheight=true;
}
if($resizewidth && $resizeheight){
if($widthratio < $heightratio){
$ratio = $widthratio;
}else{
$ratio = $heightratio;
}
}elseif($resizewidth){
$ratio = $widthratio;
}elseif($resizeheight){
$ratio = $heightratio;
}
$newwidth = $width * $ratio;
$newheight = $height * $ratio;
if(function_exists("imagecopyresampled")){
$newim = imagecreatetruecolor($newwidth, $newheight);
imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
}else{
$newim = imagecreate($newwidth, $newheight);
imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
}
ImageJpeg ($newim,$name . ".jpg");
ImageDestroy ($newim);
}else{
ImageJpeg ($im,$name . ".jpg");
}
}

if(isset($_FILES['image']['size'])){
if($_FILES['image']['type'] == "image/pjpeg"){
$im = imagecreatefromjpeg($_FILES['image']['tmp_name']);
}elseif($_FILES['image']['type'] == "image/x-png"){
$im = imagecreatefrompng($_FILES['image']['tmp_name']);
}elseif($_FILES['image']['type'] == "image/gif"){
$im = imagecreatefromgif($_FILES['image']['tmp_name']);
}

if($im){
if(file_exists("$filename.jpg")){
unlink("$filename.jpg");
}

ResizeImage($im,$resizewidth,$resizeheight,$filename); //生成小图
ImageDestroy ($im);

echo "上传成功，图片文件名是：";
echo $myname.".jpg";
}
}

//****************************************
}else{
echo "<script> window.location='login.php'</script>";
}
?>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<style type="text/css">

</style>
</head>
<body>

<form name="form1" action="" enctype="multipart/form-data" method="post">

<input name="image" type="file">
<input type="submit" value="提交">
</form>

</body>
</html>
------解决思路----------------------
你看看 product/min/ 目录下是否有生成的图片
------解决思路----------------------
ie ，Firefox，chrome试试看，这三个行的话说明代码没问题。