Php 调整/裁剪图像大小并添加空白

我有这个调整大小和裁剪功能：

$file = imagecreatefromjpeg($imagefile["tmp_name"]);

    if($imagefile["type"] == "image/jpg" || $imagefile["type"] == "image/jpeg") {
        $uploaded_file = "/var/www/adimages/".$fid."-".$imagefile["name"];
     } elseif($imagefile["type"] == "image/png") {
        $uploaded_file = "/var/www/adimages/".$fid."-".$imagefile["name"];
     }

    imagejpeg($file, $uploaded_file, 100);
    chmod($uploaded_file, 0644);

    list($width, $height, $type, $attr) = getimagesize($uploaded_file);
    $this->imageSizeW = $width; 
    $this->imageSizeH = $height;
    $this->newSizeW = 250;
    $this->newSizeH = 400;

    $aspect = $width / $height;
    $new_aspect = $this->newSizeW / $this->newSizeH;

    if($aspect >= $new_aspect) {
         $new_height = $this->newSizeH;
         $new_width = $width / ($height / $this->newSizeH);
     } else {
         $new_width = $this->newSizeW;
         $new_height = $height / ($width / $this->newSizeW);
     }

     $img_source = imagecreatefromjpeg($uploaded_file);
     $newimage = imagecreatetruecolor($this->newSizeW, $this->newSizeH);
     imagecopyresampled($newimage, $img_source, 0 - ($new_width - $this->newSizeW) / 2, 0 - ($new_height - $this->newSizeH), 0, 0, $new_width, $new_height, $width, $height);
     imagejpeg($newimage, $uploaded_file, 100);            
}

这就像预期的一样，几乎是——当它裁剪时，它会删除图像的一部分。

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我是否可以扩展/配置此功能，以便它可以调整图像大小/居中，并添加空白，使图像与原始图像一样，但仍然是250 x 400 px，而不是使用voret.net中的类上载0.32-这正是我想要的