用php调整图片宽高

<?php
/**
 * 改变图片的宽高
 * 
 * @author flynetcn (2009-12-16)
 * 
 * @param string $img_src 原图片的存放地址或url 
 * @param string $new_img_path  新图片的存放地址 
 * @param int $new_width  新图片的宽度 
 * @param int $new_height 新图片的高度
 * @return bool  成功true, 失败false
 */
function resize_image($img_src, $new_img_path, $new_width, $new_height)
{
    $img_info = @getimagesize($img_src);
    if (!$img_info || $new_width < 1 || $new_height < 1 || empty($new_img_path)) {
        return false;
    }
    if (strpos($img_info['mime'], 'jpeg') !== false) {
        $pic_obj = imagecreatefromjpeg($img_src);
    } else if (strpos($img_info['mime'], 'gif') !== false) {
        $pic_obj = imagecreatefromgif($img_src);
    } else if (strpos($img_info['mime'], 'png') !== false) {
        $pic_obj = imagecreatefrompng($img_src);
    } else {
        return false;
    }
    $pic_width = imagesx($pic_obj);
    $pic_height = imagesy($pic_obj);
    if (function_exists("imagecopyresampled")) {
        $new_img = imagecreatetruecolor($new_width,$new_height);
        imagecopyresampled($new_img, $pic_obj, 0, 0, 0, 0, $new_width, $new_height, $pic_width, $pic_height);
    } else {
        $new_img = imagecreate($new_width, $new_height);
        imagecopyresized($new_img, $pic_obj, 0, 0, 0, 0, $new_width, $new_height, $pic_width, $pic_height);
    }
    if (preg_match('~.([^.]+)$~', $new_img_path, $match)) {
        $new_type = strtolower($match[1]);
        switch ($new_type) {
            case 'jpg':
                imagejpeg($new_img, $new_img_path);
                break;
            case 'gif':
                imagegif($new_img, $new_img_path);
                break;
            case 'png':
                imagepng($new_img, $new_img_path);
                break;
            default:
                imagejpeg($new_img, $new_img_path);
        }
    } else {
        imagejpeg($new_img, $new_img_path);
    }
    imagedestroy($pic_obj);
    imagedestroy($new_img);
    return true;
}

//test
$ret = resize_image('http://static.php.net/www.php.net/images/php_snow_2008.gif', 'test.png', '300', '400');
var_dump($ret);