php imagettftext 已经转码,中文不显示,英文显示正常,求大神指导!!!

附上代码。
header("Content-Type:image/jpeg");
$str="JJJJJ";
$con = iconv("GB2312", "UTF-8",$str);
$image=imagecreate(800,600);
$bgcolor=imagecolorallocate($image, 0, 200, 200);
$fontcolor=imagecolorallocate($image, 200, 80, 80);
$font='./Public/FONTS/songti.ttf';
imagettftext($image, 80, 5, 100, 130, $fontcolor, $font, $con);
imagejpeg($image);
imagedestroy($image);

http://zhidao.baidu.com/link?url=f8X4ld9BWAf1oJ2rWeW1PzSGWdeoUGYHyQCLaRoKfQ2ezClLMLsk-AZ52jgB1QAa8k2cjlMLWwci36nVO9V4lK

http://zhidao.baidu.com/link?url=iiZEJMs4wb9G8HZ3suFREgfFWoX-5MU80ut-JvBFg6MnaceLHzvEG5p_KXWlPqmfh4FtZ2VNM3fdJ8em7WDk6B4ko8BhRWIKGxyXJOdOiDO