switch ($portf_thumbnail) {
    case 'portfolio-big':
        $grid_thumbnail = aq_resize($image_url, 566, 440, true);
        $item_class = 'item-wide';
        break;
    case 'portfolio-small':
        $grid_thumbnail = aq_resize($image_url, 281, 219, true);
        $item_class = 'item-small';
        break;
    case 'half-horizontal':
        $grid_thumbnail = aq_resize($image_url, 566, 219, true);
        $item_class = 'item-long';
        break;
    case 'half-vertical':
        $grid_thumbnail = aq_resize($image_url, 281, 440, true);
        $item_class = 'item-high';
        break;
}