我使用PHP和GD库缩略图，但我的代码将png透明度变成一个纯黑色，是否有解决方案来改善我的代码？

这是我的php缩略图制造商代码：

function cropImage($nw, $nh, $source, $stype, $dest) {

$size = getimagesize($source);

$w = $size[0];

$h = $size[1];

switch($stype) {

case 'gif':

$simg = imagecreatefromgif($source);

break;

case 'jpg':

$simg = imagecreatefromjpeg($source);

break;

case 'png':

$simg = imagecreatefrompng($source);

break;

}

$dimg = imagecreatetruecolor($nw, $nh);

$wm = $w/$nw;

$hm = $h/$nh;

$h_height = $nh/2;

$w_height = $nw/2;

if($w> $h) {

$adjusted_width = $w / $hm;

$half_width = $adjusted_width / 2;

$int_width = $half_width - $w_height;

imagecopyresampled($dimg,$simg,-$int_width,0,0,0,$adjusted_width,$nh,$w,$h);

} elseif(($w

$adjusted_height = $h / $wm;

$half_height = $adjusted_height / 2;

$int_height = $half_height - $h_height;

imagecopyresampled($dimg,$simg,0,-$int_height,0,0,$nw,$adjusted_height,$w,$h);

} else {

imagecopyresampled($dimg,$simg,0,0,0,0,$nw,$nh,$w,$h);

}

imagejpeg($dimg,$dest,100);

}

谢谢