如何从服务器生成图像的缩略图？

class Picture {

    private $image_file;

    public $image;
    public $image_type;
    public $image_width;
    public $image_height;
    public function __construct($image_file) {
        $this->image_file=$image_file;
        $image_info = getimagesize($this->image_file);
        $this->image_width = $image_info[0];
        $this->image_height = $image_info[1];
        switch($image_info[2]) {
            case 1: $this->image_type = 'gif'; break;//1: IMAGETYPE_GIF
            case 2: $this->image_type = 'jpeg'; break;//2: IMAGETYPE_JPEG
            case 3: $this->image_type = 'png'; break;//3: IMAGETYPE_PNG
            case 4: $this->image_type = 'swf'; break;//4: IMAGETYPE_SWF
            case 5: $this->image_type = 'psd'; break;//5: IMAGETYPE_PSD
            case 6: $this->image_type = 'bmp'; break;//6: IMAGETYPE_BMP
            case 7: $this->image_type = 'tiffi'; break;//7: IMAGETYPE_TIFF_II (порядок байт intel)
            case 8: $this->image_type = 'tiffm'; break;//8: IMAGETYPE_TIFF_MM (порядок байт motorola)
            case 9: $this->image_type = 'jpc'; break;//9: IMAGETYPE_JPC
            case 10: $this->image_type = 'jp2'; break;//10: IMAGETYPE_JP2
            case 11: $this->image_type = 'jpx'; break;//11: IMAGETYPE_JPX
            case 12: $this->image_type = 'jb2'; break;//12: IMAGETYPE_JB2
            case 13: $this->image_type = 'swc'; break;//13: IMAGETYPE_SWC
            case 14: $this->image_type = 'iff'; break;//14: IMAGETYPE_IFF
            case 15: $this->image_type = 'wbmp'; break;//15: IMAGETYPE_WBMP
            case 16: $this->image_type = 'xbm'; break;//16: IMAGETYPE_XBM
            case 17: $this->image_type = 'ico'; break;//17: IMAGETYPE_ICO
            default: $this->image_type = ''; break;
        }
        $this->fotoimage();
    }

    public function imagesave($image_type='jpeg', $image_file=NULL, $image_compress=100, $image_permiss='') {
        if($image_file==NULL) {
            switch($this->image_type) {
                case 'gif': header("Content-type: image/gif"); break;
                case 'jpeg': header("Content-type: image/jpeg"); break;
                case 'png': header("Content-type: image/png"); break;
            }
        }
        switch($this->image_type) {
            case 'gif': imagegif($this->image, $image_file); break;
            case 'jpeg': imagejpeg($this->image, $image_file, $image_compress); break;
            case 'png': imagepng($this->image, $image_file); break;
        }
        if($image_permiss != '') {
            chmod($image_file, $image_permiss);
        }
    }

    public function imageout() {
        imagedestroy($this->image);
    }
    public function imageresize($new_w, $new_h) {
        $new_image = imagecreatetruecolor($new_w, $new_h);
        imageAlphaBlending($new_image, false);
        imageSaveAlpha($new_image, true);
        imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $new_w, $new_h, $this->image_width, $this->image_height);
        $this->image_width = $new_w;
        $this->image_height = $new_h;
        $this->image = $new_image;
    }
}

$new_image = new Picture($filepath);
$new_image->imageresize($new_width, $new_height);
$new_image->imagesave($new_image->image_type, $newfilepath, 80);
$new_image->imageout();