php如何实现修改图片大小

$filename = "./QR/$id.jpg"; $percent = 0.4; list($width, $height) = getimagesize($filename); $new_width = $width * $percent; $new_height = $height * $percent; $image_p = imagecreatetruecolor($new_width, $new_height); $image = imagecreatefromjpeg($filename); imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height); imagejpeg($image_p,'./images/thumb/'.$id.'.jpg');