Generate XML from file in directory via PHP

I've got two folders images and big images with photos.

I want to generate an XML file with two attributes like this :

<images>
    <image source="images/image1" lightbox="bigimages/image1" />
    .....
</images>

I have something like this :

<?php

    // enter the path to the folder
    $path = "images/";


    // opendir
    $dir_handle = @opendir($path) or die("Unable to open $path");

    // table photos
    $filetypes = array("jpg", "png");

    // forming xml
    $doc = new DomDocument('1.0');


    $doc->formatOutput = true;

    // forming images

    $root = $doc->createElement('images');
    $root = $doc->appendChild($root);

    while ($file = readdir($dir_handle)) {


        $file = rawurlencode($file);

        $split = explode(".", $file);
        $ext = strtolower($split[count($split)-1]);


        if (in_array($ext, $filetypes)) {

            // additional image
            $item = $doc->createElement("image");
            $item = $root->appendChild($item);


            $file = $path.$file;

            // adding an attribute source
            $item->setAttribute('source', $file);


        }


    }




    // closure
    closedir($dir_handle);

    // Save to XML
    $doc->save("plik.xml");
    echo "plik xml wygenerowany poprawnie!!!";
?>

And now the question is how to add second attribute with path to images from "bigimages" directory.