Как скриптом создать превью изображения из детального?

    $arOrder = Array("NAME"=>"ASC");
    $arFilter = Array("IBLOCK_ID"=>34,"ACTIVE"=>"Y");
    $arGroupBy = false;
    $arNavStartParams = false;
    $arSelectedFields = false;

    $ItemsList = CIBlockElement::GetList($arOrder,$arFilter,$arGroupBy,$arNavStartParams,$arSelectedFields);

    $el = new CIBlockElement;

    while($arItem = $ItemsList->Fetch()) {
   if($arItem["DETAIL_PICTURE"] == "") continue;
   $preview_img = CFile::ResizeImageGet($arItem["DETAIL_PICTURE"], array('width'=>120, 'height'=>120), BX_RESIZE_IMAGE_PROPORTIONAL, false);
   $arLoadProductArray = Array(
       "DETAIL_PICTURE" => CFile::MakeFileArray(CFile::GetPath($arItem["DETAIL_PICTURE"])),
       "PREVIEW_PICTURE" => CFile::MakeFileArray($preview_img["src"]),
   );
   $res = $el->Update($arItem["ID"], $arLoadProductArray);
    }