Update some meta for all media library items

Only run this once! uncomment the „add_action“ then open site and then comment it out again. Watch your timeout depending on how many images you have.

/*
 * Update ALL attachments metada with Width and Height
 *
 * Important: Run Only Once
 * 
 */
//add_action('admin_init','wpse_35680_run_only_once');
function wpse_35680_run_only_once()
{   
    global $wpdb;
    $attachments = $wpdb->get_results( "SELECT ID FROM $wpdb->posts WHERE post_mime_type LIKE '%image%'" );
    foreach( $attachments as $att )
    {
        list( $url, $width, $height ) = wp_get_attachment_image_src( $att->ID, 'full' );
        update_post_meta( $att->ID, '_width', $width );
        update_post_meta( $att->ID, '_height', $height );
    }
}