php 使用GD缩小图片，使用透明格式就失真

<code>$newimg = imagecreatetruecolor($newwidth,$newheight);

//取消下面这三行设置透明格式则不会失真
imagesavealpha($newimg, true);
$trans_colour = imagecolorallocatealpha($newimg, 0, 0, 0, 127);
imagefill($newimg, 0, 0, $trans_colour);

//
imagecopyresampled($newimg,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);
</code>

<code>$newimg = imagecreatetruecolor($newwidth,$newheight);

//取消下面这三行设置透明格式则不会失真
imagesavealpha($newimg, true);
$trans_colour = imagecolorallocatealpha($newimg, 0, 0, 0, 127);
imagefill($newimg, 0, 0, $trans_colour);

//
imagecopyresampled($newimg,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);
</code>