PHP生成PDF时，背景文字怎么去掉

PHP生成PDF时，背景文字怎么去掉

下面的是原程序：
try {
$p = new PDFlib();

if ($p->begin_document("", "") == 0) {
die("Error: " . $p->get_errmsg());
}

$p->begin_page_ext(595, 842, "");

$font = $p->load_font("Helvetica-Bold", "winansi", "");

$p->setfont($font, 24.0);
$p->set_text_pos(50, 700);
$p->show_xy("Hello world (PHP)!",100 , 750 );
$p->end_page_ext("");

$p->end_document("");

$buf = $p->get_buffer();
$len = strlen($buf);

header("Content-type: application/pdf");
header("Content-Length: $len");
header("Content-Disposition: inline; filename=hello.pdf");
print $buf;

}
catch (PDFlibException $e) {
die("PDFlib exception occurred in hello sample:\n" .
"[" . $e->get_errnum() . "] " . $e->get_apiname() . ": " .
$e->get_errmsg() . "\n");
}
catch (Exception $e) {
die($e);
}

$p = 0;
?>

对于pdf格式的幻灯片，通常讲，你所说的背景文字都是加进去的图片就已经有了文字，这就需要先把图片先导出来，然后用photoshop来处理，去除文字。