query attachment images … if no attachments -> get attachments of parent page?

I use this to query all attachments of the current page or post I’m on …

$query_images_args = array(
    'post_type' => 'attachment',
    'post_mime_type' =>'image',
    'post_status' => 'inherit',
    'posts_per_page' => -1,
    'post_parent' => $post->ID //$post->post_parent
);

$attachments = get_children($query_images_args);

if ( empty($attachments) ) {
    $query_images_args = array(
        'post_type' => 'attachment',
        'post_mime_type' =>'image',
        'post_status' => 'inherit',
        'posts_per_page' => -1,
        'post_parent' => $post->post_parent
    );
}

$query_images = new WP_Query( $query_images_args );
$images = array();
foreach ( $query_images->posts as $image) {
    $images[] = wp_get_attachment_image_src( $image->ID, 'large');
}

foreach ( $images as $image) {
    if ( $image[1] >= 1024 )
        $large_images[] = $image[0];
}

if ( !empty($large_images) ):

This works perfectly and queries only the images of the current post or page.

However I have one additional thing I want this piece of code to do:

If a page has no images attached and is a “child-page” of a page that has images attached I want to query the images of the “parent-page”.

Again:

parent-page -> has images attached
child-page -> has no images attached -> should query images of the parent-page

This could be done with $post->post_parent

$query_images_args = array(
            'post_type' => 'attachment',
            'post_mime_type' =>'image',
            'post_status' => 'inherit',
            'posts_per_page' => -1,
            'post_parent' => $post->post_parent
        );

However I have no idea how to differentiate between those two cases.

If a page has images attached I want my code to be 'post_parent' => $post->ID, if a page is a child-page and has NO images attached I want the code to be 'post_parent' => $post->post_parent

Any ideas on that?