Can PNG image transparency be preserved when using PHP's GDlib imagecopyresampled?

问题：

The following PHP code snippet uses GD to resize a browser-uploaded PNG to 128x128. 以下PHP代码段使用GD将浏览器上传的PNG调整为128x128。 It works great, except that the transparent areas in the original image are being replaced with a solid color- black in my case. 效果很好，只是在我的情况下，原始图像中的透明区域已被替换为纯黑色。

Even though imagesavealpha is set, something isn't quite right. 即使设置了imagesavealpha ，也不是很正确。

What's the best way to preserve the transparency in the resampled image? 在重新采样的图像中保留透明度的最佳方法是什么？

$uploadTempFile = $myField[ 'tmp_name' ]
list( $uploadWidth, $uploadHeight, $uploadType ) 
  = getimagesize( $uploadTempFile );

$srcImage = imagecreatefrompng( $uploadTempFile );    
imagesavealpha( $targetImage, true );

$targetImage = imagecreatetruecolor( 128, 128 );
imagecopyresampled( $targetImage, $srcImage, 
                    0, 0, 
                    0, 0, 
                    128, 128, 
                    $uploadWidth, $uploadHeight );

imagepng(  $targetImage, 'out.png', 9 );

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解决方案：

参考： https://stackoom.com/en/question/8O3