建立透明png

建立透明png
 $im = imagecreatetruecolor($width,$height);
 imagealphablending($im,true);
 $transparent = imagecolorallocatealpha($im,0,0,0,127);      
 imagefill($im,0,0,$transparent);     
 imagesavealpha($im,true);

 header("Content-Type: image/png");
 imagepng($im);
 imagedestroy($im);