php writes text in specified font on image

header('Content-type: image/gif');

$image = imagecreate( 400, 200 );
$red = imagecolorallocate($image, 255,0,0);
$blue = imagecolorallocate($image, 0,0,255 );
$font = 'ARIALBD.TTF';
imageTTFtext( $image, 50, 0, 20, 100, $blue, $font, 'outofmemory.cn' );
imagegif($image);
?>

上写, php