php array_filter发送空值

Question

I have this array:

Array (
    [0] => http://localhost/cms/uploads/files/1/images/hd-allpaper-40.jpg 
    [1] => http://localhost/cms/uploads/files/1/images/IMG_6217.JPG
    [2] =>
)

Now with this code, serialize data and insert to my database :

foreach(array_filter($_POST['image_url']) as $image_url) {

    if(!empty($image_url)) {

        $url = parse_url(array_shift($_POST['image_url']));
        preg_match('/[0-99999]\/.*/', $url['path'], $matches);

        $value['gallery_data'] = serialize((array(
                                   array_filter($matches[0]), 
                                   array_values($_POST['image_title']), 
                                   array_values($_POST['image_alt'])
                                 )));

        print_r $value['gallery_data'];

    }

}

But when i print_r $value['gallery_data']; matches[0] send empty value.

EDIT : when replace $matches[0] with $_POST['image_url'] my code worked true.

var_dump(matches[0]):string(28) "1/images/hd-wallpaper-40.jpg" string(21) "1/images/IMG_6217.JPG"

how do fix this problem ?!