<?php
$image = imagecreate(200,200);
$white = imagecolorallocate($image,0xFF,0xFF,0xFF);
$black = imagecolorallocate($image,0x00,0x00,0x00);
imagefilledrectangle($image,50,50,150,150,$black);
header("Content-Type:image/png");
imagepng($image);
?>
这段代码要画出下面的图形
实际效果却是
请问错在了哪里?怎么修改?