PHP GD库处理JPG图片大小变模糊的解决办法

<?php
header("Content-type: image/png");

$temp_width = 150;
$temp_height = 180;

$img_path = "test.jpg";
$img_path2 = "test2.jpg";

$im = @imagecreatefromjpeg($img_path);

$temp_img=imagecreatetruecolor($temp_width,$temp_height);
imagecopyresampled($temp_img,$im,0,0,0,0,$temp_width,$temp_height,$temp_width,$temp_height);
//echo $temp_img;
//imagejpeg($temp_img);
imagepng($im,$img_path2);

/*
imagecopyresized($temp_img,$im,0,0,0,0,$temp_width,$temp_height,$srcW,$srcH);
$ni=imagecreatetruecolor($width,$height);
imagecopyresampled
$res = function_exists('imagecreatetruecolor');
var_dump($res);
*/
?>
<br />
<img src="http://www.jbxue.com/ /test.jpg"/>