imagettftext —写入中文导致乱码,GD库啥都文件配置好了,英文可以,换成中文就乱码.....求解决

<?php
session_start();
$image=imagecreate(320, 210);
$bg=imagecolorallocate($image, rand(252,255),rand(252,255),rand(252,255));
$font='ttfs/simhei.ttf';
$word='猪';
$word=iconv('GB2312', 'UTF-8', $word);
for($i=0;$i<20;$i++){
$color=imagecolorallocate($image,rand(0,233),rand(0,211),rand(0,100));
imagettftext($image,rand(1,20),rand(0,45),rand(0,150),rand(0,100),$color,$font,$word);
}
header("Content-type: image/png");
imagepng($image);
imagedestroy($image);