质量差的jpeg在GD库使用时调整大小。错误的步骤？

Question

所以我有以下脚本来调整传入的jpg的大小并以新的大小将其保存到服务器。创建的jpg文件质量很差，即使我在imagejpeg上制作了90的质量。我想知道我是否在早些时候搞砸了。

// Get new sizes
    list($width, $height) = getimagesize($filename);
    $percentW=298/$width;
    $newwidth = $width * $percentW;
    $newheight = $height * $percentW;

    // Creating a blank canvas to put the new file. Is this an extra step?
    $thumb = imagecreatetruecolor($newwidth, $newheight);
    $source = imagecreatefromjpeg($filename);

    // Now I create the resized photo with the needed width and height on the blank canvas with the source file resized
    imagecopyresampled($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

    // Output to server, define 90% quality. My guess is the quality is destroyed before now.
    imagejpeg($thumb,"../../uploads/buckets/" . $_POST["bucket"] . "/" .$fileNameBucket,90);
    imagedestroy($thumb);

在将文件输出到服务器之前，我是否搞砸了质量？我应该使用resample而不是resize吗？我很难使用GD库，所以ImageMagick不是一个选项。感谢。