php修改上传图片大小的方法

<?php
// This is the temporary file created by PHP
$uploadedfile = $_FILES['uploadfile']['tmp_name'];
// Create an Image from it so we can do the resize
$src = imagecreatefromjpeg($uploadedfile);
// Capture the original size of the uploaded image
list($width,$height)=getimagesize($uploadedfile);
// For our purposes, I have resized the image to be
// 600 pixels wide, and maintain the original aspect
// ratio. This prevents the image from being "stretched"
// or "squashed". If you prefer some max width other than
// 600, simply change the $newwidth variable
$newwidth=600;
$newheight=($height/$width)*600;
$tmp=imagecreatetruecolor($newwidth,$newheight);
// this line actually does the image resizing, copying from the original
// image into the $tmp image
imagecopyresampled($tmp,$src,0,0,0,0,$newwidth,$newheight,$width,$height);
// now write the resized image to disk. I have assumed that you want the
// resized, uploaded image file to reside in the ./images subdirectory.
$filename = "images/". $_FILES['uploadfile']['name'];
imagejpeg($tmp,$filename,100);
imagedestroy($src);
imagedestroy($tmp);
// NOTE: PHP will clean up the temp file it created when the request
// has completed.
?>