PHP创建下载链接

<?php
    $file = SEVENCE_DATA_ROOT."/resource/devdemo/promo_card.tiff";
    header('Content-Description: File Transfer');
    header('Content-type: application/tiff');
    header("Content-Type: application/force-download");// some browsers need this
    header("Content-Disposition: attachment; filename=promo_card.tiff");
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));
    ob_clean();
    flush();
    readfile($file);
    exit;
?>

我的问题是下载的图像无法查看。有人能帮我解决这个问题吗?